Method and apparatus for facilitating use of hypertext links on the world wide web

ABSTRACT

A database server contains pointers to useful information, such as on the World Wide Web. Users of the server may have hypertext links added automatically into documents they submit. Users may additionally contribute to the link database, thereby extending it, and may add additional qualifying information pertaining to the links.

1 CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of Ser. No. 09/412,248 filed Oct. 5,1999, now U.S. Pat. No. 6,772,139 issued Aug. 3, 2004, which claimspriority from U.S. Provisional Patent Application No. 60/103,089, filedOct. 5, 1998, which is incorporated herein by reference.

2 BACKGROUND OF THE INVENTION

2.1 Field of the Invention

The present invention relates to facilitating access to information overa computer network such as the Internet. More particularly, the presentinvention relates to technology for partially automating the linking ofdocuments on the World Wide Web by authors of Web content. Suchtechniques are particularly useful for more easily creating richlyinterconnected information on the Web.

2.2 Description of Related Art

The World Wide Web provides an enormous distributed database ofinformation interconnected physically by the Internet. One of the maindifficulties for users of the Web is finding needed information out ofthe tremendous quantity of information that is available. Variousmechanisms have been developed to address this problem.

One mechanism for facilitating access to information on the Web is theindex website. An index website is typically a server computer connectedto the World Wide Web which maintains an index of Web content that canbe searched in various ways by users (clients) connected to the serverover the Internet. Indexes are often updated automatically by means of“spiders” which systematically explore the Web looking for new orupdated content. Most search engines also provide means for users toinstall information to be indexed, so that such information may beindexed immediately without waiting for a spider to find it. An exampleof a premier search engine is the “Alta Vista” website, accessible onthe Web at the Universal Resource Locator (URL) addresshttp://www.altavista.com.

A difficulty with search engines is that search results typicallycontain too much undesired information as well as the desiredinformation. This occurs because the information content of the Web isvast, and because it is difficult for users to construct searchparameters in such a way as to pass most desired content while rejectingmost undesired content. As a result, users typically must spend a lot oftime sifting through search-engine results and/or refining theirsearches with additional restrictions in the search parameters.Additionally, the information stored in the index is not organized in aform suitable for browsing in a logical order.

Another mechanism developed to facilitate access to information on theWorld Wide Web is the directory website which presents a hierarchicaldirectory of information that can be browsed by the user. Premier sitesof this nature include Yahoo (<<http://www.yahoo.com>>), Netscape(<<http://www.netscape.com>>), and Excite (<<http://www.excite.com>>). Avisitor to such a site is first presented with a top-level list oftopics. Choosing a topic by clicking on a topic's hypertext link withthe mouse produces a list of subtopics, and so on, until a final levelis reached at which useful information is displayed about the topic, orelse a remote website pertaining to that topic is visited. Directorycompanies such as Yahoo typically have teams of editors who explore theWeb looking for content suitable for reference at their site, and theseworkers perform a function analogous to the automatic “spiders” used byautomated index websites. Like the search engines, directory websitesnormally support searching within the directory site, thus producingsearch results of generally higher quality and less “clutter” thantypically encountered on an index site. Also like index websites,directory websites typically allow submission of content for reference,subject to editorial consideration. Thus, directory websites improveover index websites by providing editorial selection, logicalorganization, and browsing capability, all of which are absent intypical index websites.

A first difficulty, however, with directory websites is that they cannotreasonably keep up with the vastness of the information on the WorldWide Web by means of manual editorial selection. As a result, directorywebsites tend to offer far less information relative to index websites.A second difficulty with directory servers is that their content isproprietary and controlled by a team of editors at one company. Thiseditorial control, while ensuring consistently high quality on the site,makes it difficult and sometimes even infeasible for an informationprovider to obtain a desired listing in the hierarchical directory. Onedirectory site that addresses this difficulty is the Open Directoryproject (<<http://dmoz.org/>>); The Open Directory allows any user onthe Internet to become an “editor” for a particular topic at the site. Athird difficulty related to the first is that typical directory sitesare extremely broad in scope, contributing to the absence of specializedinformation that is not of interest to a wide general audience.

A difficulty with both index and directory websites is that informationis presented without regard to the user's level of education. It istherefore often possible for a high-school senior working on a bookreport, for example, to encounter information understandable only by agraduate student in a specialized field. There is similarly normally nomeans for selecting information according to its type or source or otherpotentially desirable criteria.

To assist users in selecting sources of information, some websitesprovide a user rating system (or “scoring system”) to which any user maycontribute. An example of this mechanism is seen in the onlinebook-store website <<http://www.amazon.com/>>. Amazon allows any user tocontribute a “book review” and an overall rating on a five-star scale.The average rating is displayed for each book, and books which match theuser's search criteria are displayed sorted according to decreasingscore (and possibly other criteria such as the number sold). Aninteresting feature of the Amazon rating system is that it isdemocratic, allowing the vast quantity of World Wide Web users tojointly develop a ranking of the information sources (in this casebooks). Such a scheme addresses the difficulty of sorting throughenormous quantities of information by harnessing a potentially enormousbase of users as contributing editors, in effect. A difficulty withrating systems is that they are generally used only at the site wherethe ratings are collected, and no mechanism is provided for making useof the ratings elsewhere, such as in other documents on the Web linkingto the same information.

An important mechanism integral to the function of the World Wide Web isthe HyperText Markup Language (HTML) which is a text format supported byWeb browser programs (such as Netscape Navigator or Microsoft InternetExplorer). A more recent variant called XML is now gaining support, andits function is similar to that of HTML for present purposes. HTMLprovides for the specification of hypertext links in Web-page textdisplayed by the browser. At a minimum, a hypertext link consists oftext to be displayed by the browser and a link target which is usuallynot displayed. For example, the HTML code<a href=“http://www.w3k.org”>W3K website</a>contains the text (also known as the anchor) “W3k website”, while thelink target is http://www.w3k.org which is a URL pointing to the W3Kwebsite. Thus, the link target is normally addressed by a URL pointingto information on the Web about the displayed word or phrase. (Thecomplete HTML format specification may be found online at the URLhttp://www.w3.org/.) To the browser user, the anchor text of a hypertextlink as above appears in a Web-page display as an underlined word orphrase, e.g.,Visit the W3K website for more information regarding automatic linkinstallation.and usually in a different color than normal, unlinked text. By clickingon the hypertext link with the mouse, the user directs the browserprogram to “follow the link” by “navigating” to the URL associated withthe link. The link-target URL may point to another Web page anywhere onthe World Wide Web, or it may simply point to another location withinthe same electronic document. Hypertext links in HTML documents make itmuch easier for the user to explore the World Wide Web by visiting Webpages and clicking on the links found therein. Web browsers further makeit easy to return to the page containing the link by using the “back”button, or the “history” list of visited pages maintained by thebrowser.

A difficulty with hypertext links is that they must be laboriously addedby Web content providers. Typical HTML editors merely provide adata-entry form in which the URL for the link target can be typed. Asecond shortcoming of HTML and Web browsers is that there is no standardmechanism for specifying link properties such as educational level, typeof resource, information source, or the like, which could be supportedby Web browsers to give the user finer control of link display based onlink properties. After the links are typed in, they must be maintainedas their URLs change, and as new and better link-targets becomeavailable. There is therefore a need for automated assistance withentering, maintaining, and improving hypertext links in documentsintended for a hypertext document environment such as the Web.

3 SUMMARY OF THE INVENTION

It is a primary object of the present invention to facilitate theaddition of hypertext links (also called “hyperlinks,” “links,” or“definitions”) to documents intended for access on the Internet via theWorld Wide Web. Accordingly, the present invention is designed toprovide a link installation service which automatically installshyperlinks within information submitted to the service by hypertextauthors. Submissions may be in HTML format, plain ASCII format, LaTeXsource format, or a variety of additional formats to be added in thefuture. The output returned to the user may be in either HTML or LaTeXsource format (which may be compiled into HTML format). Criteria canoptionally be specified which govern the installation of hyperlinks.

The invention further provides selectable databases of hyperlinks,organized by category (or “context”), which can be optionally selectedfor automatic link installation. It is further provided that contentdevelopers may add their own links to the existing link databases, andthey may additionally create new link databases and specify theirrelation to the existing link databases. Contributing users arepreferably required to have a known, verified email address. A user witha verified email address is called a “known user”. The invention furtherprovides means for browsing the link databases in a logically organized,hierarchical tree structure, wherein higher-level nodes correspond tomore general contexts, and lower-level nodes correspond to morespecialized contexts. The link databases can additionally be searchedfor keyword matches within component fields. Users may provide ratingsand/or reviews for individual links in the link databases.

The hyperlink databases of the present invention support variousoptional “properties” associated with each hyperlink. One such property,useful in the development educational content, is a level designationwhich indicates the educational level required for best understanding ofthe link-target information. Additional optional properties include thelanguage of the content (such as English), a viewer suitability ratingsuch as exists for movies (PG-13, R, etc.), and properties defined bythe user. Link properties can be specified by users to control theautomatic installation of links, and/or to control what is displayedwhile browsing the link databases.

Educational levels not specified on submission are estimated based onthe level of links found within the link target document. As a result,every link in the link database is assigned either an educational level,either manually or automatically. Determining levels automaticallydetects any “cycles” in the link database. (A “cycle” occurs whendocument A links either directly or indirectly to document B, anddocument B links either directly or indirectly to document A.) Cycledetection can help content providers eliminate inadvertent “forwardreferences.” Means are provided for marking forward-reference links insubmitted documents so that educational level will not be affected.Cycle-free systems of links can be more effectively used as a basis foronline course materials.

Another feature of the present invention is the ability for users torate (or score) the quality of any link in the database and/or to submita written review of any link. The quality ratings may be averagedtogether and used to determine the relative ordering of the links whenthere are multiple link targets for the same word or phrase (“competingdefinitions”). In the typical case of HTML format, features of theJavaScript scripting language may be used to provide convenient accessto multiple link targets, ranked according to score. Alternatively, thelatest ranked list of competing definitions may be maintained on acentral server on the Web, with the installed link pointing there,instead of containing only a snapshot at the time of link installation,which may rapidly go out of date. Alternatively, the currently highestrated link may be installed in the user's Web document for eachrecognized topic.

4 BRIEF DESCRIPTION OF THE DRAWING FIGURES

FIG. 1 shows an example initial Web page seen by a visitor using a Webbrowser to access the online version of the service.

FIG. 2 shows a Web page giving an overview of the capabilities of theonline service.

FIG. 3 shows an example Web top-level page seen while browsing thehyperlink databases.

FIG. 4 shows an example lower-level page seen while browsing thehyperlink databases, in which the context has been narrowedconsiderably.

FIG. 5 shows an example browsing view at the level of a key phrase inwhich all displayed links are interpreted as “definitions” for the keyphrase.

FIG. 6 shows an example form for adding a new link (definition) to thelink database for the current key phrase.

FIG. 7 shows a Web page for submitting text for link installation.

FIG. 8 depicts the tree structure of the hierarchical link database.

5 DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The following is a description of the best presently contemplated modesof carrying out the invention. The descriptions are not to be taken in alimiting sense but are made for the purpose of illustrating the generalprinciples of the invention. It is particularly noted that the inventionmay be implemented in a variety of different file formats, databasetechnologies, search and replace methods, computer processors and systemarchitectures, host operating systems, network protocols, user-interfaceframeworks, and the like.

5.1 Cli nt-S rver Architecture n th World Wide W b

FIG. 1 illustrates how a World Wide Web “home page” might appear on awebsite embodying the principles of the present invention. The user hasseveral choices of where to “navigate” next:

-   -   The first choice 101 is a hypertext link entitled “Learn about        the W3K,” where in this example, “W3K” is an acronym standing        for the “World Wide Web of Knowledge.” If this choice is        selected by clicking the mouse on the underlined text, the        visitor “navigates” to the Web page shown in FIG. 2 which        provides an overview of the online service provided by the W3K.        In particular, it is explained how submitting plain text 110 to        the W3K server will result in hyperlinked text 111 being        returned to the user. A summary 115 of high-level functions is        also provided in FIG. 2.    -   The second choice in FIG. 1 is a hypertext link 102 entitled        “Browse the W3K.” If this choice is selected by clicking the        mouse on the underlined text, the visitor “navigates” to the Web        page shown in FIG. 3 supporting browsing of the hyperlink        databases, as described further below.    -   The third choice in FIG. 1 is a hypertext link 103 in which the        text displayed by the Web browser is “Install W3K links in a Web        document.” If this choice is selected, the visitor is taken to        the Web page of FIG. 7 where the user can submit text for link        installation in a variety of formats. The text is returned to        the user by the server with hypertext links installed according        to the user's specifications. Link databases to be searched can        be collected into a list during the browsing operation.    -   The fourth choice, “Add to or Edit the W3K,” is a link 104 to a        Web page for editing the link databases. Editing operations        include including submitting new links, creating new link        categories, and changing previously submitted links or link        properties. These editing functions are also available while        browsing the databases.    -   The fifth and final choice, “Search the W3K Dictionaries,” is a        link 105 to a Web page for specifying search criteria in terms        of link properties. The search collects together all links in        the link databases matching the search criteria, and displays        them organized by properties according to user specifications.        The search feature is useful for collecting various link subsets        together for various purposes including link installation,        editing link properties, and other functions involving groups of        links. As an alternative to a list display format, a sparse        context hierarchy can be generated, containing only the database        information matching the search criteria; the sparse hierarchy        can then be conveniently browsed by the user.

These functions are described in further detail below.

5.1.1 Overview and Terminology

This section introduces the main terms which will be used hereafter.

Hierarchical Contexts

The link databases are organized hierarchically according to category,somewhat like the Dewey decimal system for library organization. Eachcategory (or “directory”) is interpreted as a context analogous to afield of study. Each context may itself contain any number of contexts(“subcontexts,” or “subdirectories”), and it may additionally contain adatabase of information pertaining to that context (which may be aimplemented in a file in that directory).

The particular sequence of directories obtained by visiting onesubdirectory after another is called a path. Every context may beidentified by the directory path that reaches it from the top level.Thus, the set of all contexts form a “tree structure” analogous to thehierarchical file systems used by all major computer operating systemsat the present time.

Dictionaries

A link database (or “dictionary”) preferably comprises a list of(key,URL) pairs. A key (or “key phrase” or sometimes “word”) identifiesa topic or concept, and the URL points to information about that topicon the Internet. In a loose analogy with an ordinary dictionary, the keyis the “word being looked up”, and the URL points to its “definition”.However, unlike an ordinary dictionary, the (key,URL) pairs in the linkdatabase are interpreted within the particular context associated withthe directory containing that dictionary. In a somewhat better analogywith a technical encyclopedia in a particular field, the key correspondsto the noun phrase identifying a technical topic for which an articleexists in the encyclopedia, the URL may correspond to the page number onwhich the article begins, and the context may correspond to thetechnical field for which the encyclopedia was written.

Because dictionaries are interpreted in a particular context, alternatedefinitions are not allowed. In other words, a context is preferablysufficiently narrow such that all terms (words or key phrases) in thatcontext have a unique meaning. Ordinary “flat” dictionaries mustaccommodate alternate definitions for a single word, while “hierarchicaldictionaries” need not. Thus, if a term is found to have a secondmeaning in a particular context, it is time to create one or moresubcontexts in which that term is disambiguated.

Synonyms

A single URL can provide only one “definition”. However, a single URLcan be used to “define” any number of key phrases, which are thenregarded as synonyms. Often the title of the addressed HTML page on theWeb is the “key phrase” that is “defined” by the URL. When there areseveral (key,URL) pairs having the same URL, the different keys aretreated as alternate phrasings for the same concept or topic, and aresaid for form a synonym group. The following example dictionary entriesprovide an example of a synonym group:KEY=Taylor Series ExpansionURL=<<http://www.mathworld.org/analysis/TaylorSeries.html>>KEY=Taylor ExpansionURL=<<http://www.mathworld.org/analysis/TaylorSeries.html>>KEY=Taylor SeriesURL=<<http://www.mathworld.org/analysis/TaylorSeries.html>>

Order is important in the dictionary because “the first match wins”during automatic link installation. For example, with the aboveordering, the key phrase “Taylor Series Expansion” will match beforechecking for “Taylor Expansion” or “Taylor Series”. Ordering equivalentkey phrases from longest to shortest ensures that the longest possiblematch will occur in documents submitted for link installation.

Synonyms can be listed in a link's properties, or they can simply beentered as additional link entries pointing to the same link target(URL), since links take up relatively little space.

“Key Phrase” Directories

A “key phrase” may be understood as a bottom-level subdirectory of thecontext tree. A key-phrase directory holds a dictionary (link database)containing at least one link. This database may be implemented as a fileresiding in a directory having a name derived from the key phrase.Preferably, however, all key phrases in a particular context (togetherwith their links), plus perhaps additional contexts, are implemented ina single larger database file in the parent context directory. Forsimplicity, however, a key phrase will nevertheless be consideredlogically to be a bottom-level directory (leaf node) in the hierarchicalcontext directory, irrespective of implementation details associatedwith the use of a hierarchical file system.

All of the links in the key-phrase directory are interpreted ascompeting sources of information on the one topic identified by the keyphrase. The tangible difference between a key-phrase directory and acontext directory is that the key-phrase directory has no subcontexts,only links. Thus, a bottom-level directory in the context tree hierarchy(a “leaf node” of the context tree) corresponds to a single concept ortopic, and all of the (key,URL) pairs in its dictionary pertain to thatone topic. The number of distinct URLs present is the number ofcompeting sources of information.

Perhaps the simplest means for handling synonyms is to add a key-phrasedirectory for each alternate phrasing of each topic. Because order isimportant when traversing a synonym group, the context-treeimplementation must provide a means for ordering sub-directories, atleast when those sub-directories correspond to key phrases.Alternatively, an ordered link database file may reside in the contextdirectory containing the key phrase, and include all other key phrasesin that context as well (including synonyms); the key phrase(s)corresponding to each link may be stored as link properties.

In the preferred embodiment, synonyms are not handled as separatekey-phrase directories. Instead, a single representative is selected(usually the most descriptive or canonical), and all other equivalentphrasings (synonyms) are listed in a separate synonym file in thekey-phrase directory. (Order is carefully preserved.) During browsing,synonyms are displayed at the bottom of the key-phrase page.

Context Synonyms

The preferred embodiment also supports context synonyms, as opposed tokey-phrase synonyms just described. Context synonyms are presentlyimplemented using symbolic links in a UNIX file system implementation ofthe context tree. As an example, the context hierarchy below illustratestwo different paths to the subcontext (directory) “Sound_Synthesis”,where the notation “->” indicates a symbolic link, as is typically donewhen listing files in a UNIX file system:

Humanities Music Computer_Music Sound_Synthesis Engineering ElectricalSignal_Processing Sound_Synthesis −>/Humanities/Music/Computer_Music/Sound_Synthesis

In this example, the “true parent” of the node Sound_Synthesis isComputer_Music, while the parent Signal_Processing is a “linked parent”.There can be any number of linked parents, but only one true parent.

Symbolic links provide a means for reaching multidisciplinary fields bybrowsing the constituent fields in a top-down way. At any time, asymbolic link may be deleted and replaced with a copy of some or all ofthe directory which was formerly linked (possibly utilizing symboliclinks at a lower level). In this way, closely related contexts may startout as identical, but later may evolve into separate collections, as themaintainers see fit.

Context Dictionaries

The dictionary corresponding to a particular context is defined as theunion of all key-phrase dictionaries in that context. In other words,the dictionaries belonging to all key-phrase subcategories in theparticular context are logically concatenated together into one largedictionary, with additional dictionary entries added for all synonyms.This dictionary is referred to as the “context dictionary”. The order inwhich the key phrases are concatenated is prescribed.

When installing links in submitted documents, several contextdictionaries are normally combined together to form a larger “aggregatedictionary” which is what is used for link installation. A typicalaggregate dictionary consists of the context dictionary for the “currentcontext” (established, e.g., by browsing), followed by thecontext-dictionaries of all subcontexts (usually not in any particularorder, unless explicitly listed by the user), then followed by thecontext dictionary of the “true parent” context, followed by the contextdictionary of the true parent's true parent, and so on, until thecontext dictionary of the top-level directory is appended (whichcontains extremely generic terms). Linked parent dictionaries may alsobe added in where desired. Since order is respected during linkinstallation, definitions provided in the “current context” will receivefirst precedence, followed by definitions occurring in subcontexts(which are considered within the current context), followed by the moregeneric definitions of parent contexts. Since “the first match wins” inlink installation, generic terms defined in parent contexts are“overridden” by more specialized definitions of the same terms of art inthe current context. For example, the word “resolution” might be definedat the top level as the first definition appearing in an ordinarydictionary of the English language, while in the context of “. . ./Signal Processing/Spectrum Analysis” it would be given its more arcanedefinition regarding the resolving power of a short-time Fouriertransform.

5.1.2 Browsing the Link Databases

There several benefits to providing browsing of the link databases:

-   -   it provides a unique educational resource which organizes        valuable information on the Web in a manner especially well        suited for educational purposes;    -   it provides a convenient means for learning what links are        available for installation in documents;    -   it provides a convenient means for collecting context        dictionaries for subsequent use in automatic link installation.        While browsing, links and/or entire context subtrees can be        marked for inclusion or exclusion in subsequent automatic link        installations;    -   it provides a convenient means for navigating to contexts in        which subcontexts and/or key-phrases can be added and/or edited        by the user, or to key-phrase directories in which links can be        added and/or edited and/or rated; and    -   by displaying links selectively according various link        properties, browsing provides a means for viewing useful link        subsets, such as all links entered by the user or user's group.

Link database browsing support on the server may be implemented in avariety of ways. As an example, there are commercially available scriptswhich implement directory websites, such as the links-2.0 scripts fromGossamer Threads, Inc., and such scripts can be adapted to implement thehierarchical dictionary of the present invention. FIGS. 3 and 5illustrate the appearance of such a browsing system. Alternatively, onemay use HTML SELECT pop-up menus, which are dynamically generated fromthe current directory contents. However, for performance reasons, staticHTML pages are preferable over dynamic HTML generated by the server,when feasible. To provide more context and ease of navigation, thedatabase directory structure may additionally be displayed in a fixedHTML frame on the left, as is currently done on many websites. Forexample, the way directory trees are displayed on the left in MicrosoftWindows Explorer is a good model.

FIG. 3 illustrates a Web page display at the start of browsing. Thetop-level context is displayed. In this simplified example, only fourtop-level subcontexts are offered (Computing 131, Education 132, Legal133, and Music 134). Each of these words is a hypertext link, which canbe clicked with the mouse to navigate to the associated sub-context. Forexample, clicking on Music 134, then on “Computer Music” (which isavailable in the Music context), then on “Signal Processing”, thenfinally on “Sound Synthesis” produces the page shown in FIG. 4.

5.1.3 The Standard Browsing Menu

Near the top of each page during browsing is a set of hypertext links130 separated by a vertical bar ‘|’. This is the “standard menu”appearing at the top of every page while browsing the W3K website and atother times as well. Each of these links allows the user to carry outsome available function.

The “W3K Home” link in the standard menu 130 takes the browser back tothe initial W3K home page illustrated in FIG. 1, as does clicking on theW3K logo.

The “Browse from Top” link in the standard menu 130 navigates to thetop-level browsing page shown in FIG. 3.

The “Select Hierarchy” link navigates to a page where a differentcontext hierarchy can be selected for browsing. There is only oneprimary public context hierarchy (the one reached from the second choice102 in FIG. 1). However, individual users and groups of users can set upcontext hierarchies for their own purposes, without having to worryabout fitting into the ever-expanding primary public context hierarchy.If well known “language localization” methods are not available, aspreferred, to provide alternate language selection for each Web page inthe public hierarchy, alternate hierarchies can be used to supportalternate languages. Alternate hierarchies can be designated by theircreators as public (anyone can add to it), restricted (anyone can readit, but only the owner(s) can write it), or private (only the owner(s)can read or write it). The owners include the creator and members of anygroups listed by the creator as being co-owners.

The “Install Links” link in the standard menu 130 navigates to the formprovided for submitting documents for link installation, which will bedescribed further below.

The “Add Subcontext” link navigates to the form provided for creating anew subcontext within the current context. Since FIG. 3 is at thetop-level context, this operation is only allowed in a public hierarchyfor a select group of “trusted” users.

The “Add Key-Phrase” link leads to the form for adding a new key phrasein the current context. At least one definition link is required whenadding a new key phrase. At the top level of the public hierarchy, thisoperation is restricted to trusted users since any key phrases appearingat the top of the hierarchy are “generic terms” having definitions whichare independent of context. Truly global key phrases such as domainnames and trademarks are appropriate at the top level.

The “Add Definition” link is for adding a new definition for a keyphrase. This entails supplying a URL which points to information aboutthe URL and some other information, as will be later described. Thus,the number of distinct URLs in the set of URLs associated with aparticular key phrase can be increased from 1 (its usual initial value)to any number by adding more definitions. The “Add Synonym” link in thestandard menu 130 allows the addition of a key phrase to a list of“synonyms” for an existing key phrase. A synonym can also be constructedfor a context. Synonyms will be described further below.

“Submit Dictionary File” provides convenient submission of a largenumbers of links (key phrases and definitions) as well as the ability tospecify context path for each one, as will be described. It isadditionally possible to display specified contexts and contextsselected for link installation in the form of a dictionary file. Forexample, a user can perform a search in order to collect all linkscontributed by that user, display the results as a dictionary file, savethe dictionary file on his or her local computer, perform any desiredediting operations, and submit the edited dictionary file back to theserver to update his or her links on the server.

“Modify Additions” allows the user to edit (modify or delete) anyinformation he or she submitted to the W3K site. In particular, it ispossible to modify link properties, delete a link, delete a context orkey-phrase directory wholly owned by the user or user's group, and soon. A user belonging to one or more groups may edit any informationsubmitted by anyone in any of those groups. A set of records to beedited can be created by means of the search facility. A record may holdthe information associated with a link, key-phrase directory, or contextdirectory.

“Select Context” selects the “dictionary” associated with the currentcontext for inclusion in subsequent “link installation”. The contextdictionary normally includes each key phrase in the current contexttogether with at least one definition for each key phrase. It may alsoinclude similar information from parent contexts and subcontexts, aswill be discussed. Thus, the aggregate dictionary used in linkinstallation is like a kind of “shopping cart” that can be filled withcomponent dictionaries found while browsing around the contexthierarchy; in this analogy, “items to be purchased” correspond to thedictionaries to be used in link installation.

It is also possible to assemble various context directories into anaggregate dictionary for link installation without browsing by simplyproviding a context dictionary list, or by selecting contexts from anumber of SELECT menus in HTML listing all available contexts. After thecurrent context is selected, the “Select Context” link changes to“Deselect Context”, so that clicking on it takes the current context outof the aggregate link installation dictionary.

Selection configuration information lower in the hierarchy is notmodified when excluding a context, so that re-selecting the contextallows the contained selection configuration to become active onceagain. During link-installation (FIG. 7), it is possible to override allsuch selection information by simply specifying an explicit list 75 ofcontext dictionaries, or selecting “All W3K contexts” in the form entryfor contexts 179.

Browser “cookies” are very useful for storing the context searchpreferences for the user across sessions; since many tend to work in oneor a few fields, it is often the case that the contexts used for linkinstallation do not change very often. Browser cookies are simplyinformation stored on the user's computer (the client computer) by theserver; cookie files are supported by the major Web browsers such asNetscape Navigator and Microsoft Internet Explorer. If cookie files arenot available for any reason (they can be disabled by the user),preference information can be stored on the server indexed by the user'semail address, which is unique among users.

“Browse All Selected” places hierarchy browsing in a special mode inwhich only the currently Selected contexts and links are visible. Thiscan also be reversed so that only deselected contexts are visible.(Sometimes it is helpful to go back and forth.) This feature can helpthe user more quickly review what link databases (“key-phrases” and“definitions”) have been selected for link installation.

“Edit All Selected” is similar to “Modify Additions” except that insteadof determining the list of database elements to be edited by using asearch (or direct specification), it is initialized from the set ofselected links owned by the user and/or groups to which the userbelongs.

“What's New” creates a list of all contexts, key phrases, or definitionswhich have been added recently to the system.

“What's Cool” creates a list of all contexts, key phrases, ordefinitions which have been receiving relatively high traffic (“hits”)recently.

“Top Rated” creates a list of highest ranked links in the database.These are generally excellent home pages, tutorials and the like onvarious topics.

“Email Updates” allows the user to subscribe to the W3K newsletter.

“Random Link” takes the user to a randomly chosen definition link.

“Search” supports general search for information within the currentcontext and beyond.

5.1.4 Context Path Display

While browsing, the “context path” 140 (FIG. 4) is displayed just belowthe standard menu 130, with each path element separated by a colon ‘:’.In FIG. 4, for example, the context path is displayed as“Top:Music:Computer Music:Signal Processing:Sound Synthesis.” Clickingon the “Lagrange Interpolation” key-phrase 144 in this context takes thebrowser to the definition page for Lagrange Interpolation shown in FIG.5.

5.1.5 Search Form

Below the horizontal line in FIG. 3 is a search form. Typing text intothe field and clicking on the “Search!” button results in a dynamicallygenerated web page listing all links (in all contexts) matching thesearch criteria. More refined searches can be carried out by firstselecting the “More search options” link. Since links have quite a fewproperties (to be discussed), searches can be honed rather finelywithout relying entirely on typical means for selecting a subset of allnames and phrases within contexts, key-phrases, and definitions.

5.1.6 Topics under a Context

FIG. 4 displays the contents of the context-path/Music/Computer_Music/Signal_Processing/Sound_Synthesis.

We see that the “Sound_Synthesis” context contains two subcontexts“Acoustic Instruments” 148 and “Vintage Methods” 149.

In addition to subcontexts, there is a list labeled “Words and phrasesdefined in context Sound Synthesis” 141. (For greater convenience whenbrowsing contexts, browsing can be configured to show only a single linkto the key-phrase list on a separate page.) The phrases listed include“Commuted Synthesis” 142, “Physical Modeling” 145, and “LagrangeInterpolation” 144.

Technically, as far as the browsing function is concerned, “words andphrases” (key phrases) are similar to “subcontexts”. However, keyphrases are browser categories with no subcategories, only links, whilecontexts are browser categories containing subcategories (eithersubcontexts or key phrases). The links under a key-phrase are treated as“competing definitions” for that key phrase.

FIG. 8 illustrates the relationships among contexts, key phrases, anddefinitions. The top level context 180 is the root node of the treestructure defined by the hierarchical link database. There can be anynumber of subcontexts or key phrases under the top level context 180. Inthe example of FIG. 8, there are two subcontexts, “Intermediate Context1” 181 and “Intermediate Context 2” 182. Since these are contextdirectories, they each may contain any number of subcontexts and/or keyphrases. In the present example, there are two key phrases 183 and 184in the first subcontext 181 and one synonym group 185 (two equivalentkey phrases) in the second context 182. A key phrase must have at leastone definition (link) associated with it. In the present example, “KeyPhrase 1” 183 contains three competing definitions 186, “Key Phrase 2”184 contains four competing definitions 187, while the synonym group 185consisting of “Key Phrase 3” and “Key Phrase 4” contains two definitions188 to choose from for that synonym group. Since order is important, wemay choose a consistent ordering convention for tree diagrams in whichthe ordering of all subnodes of a node is defined as left to right in adiagram as in FIG. 8.

Note also in FIG. 4 that the “Sound Synthesis” 141 context includes onesynonym 143. This is a context synonym identified by the pathEngineering:Signal Processing:Sound Synthesiswhich can be thought of as a different context path to the same place. Acontext synonym can be thought of as a “symbolic link,” in the sense ofa UNIX file system, from one “context directory” to another. It is oftenappropriate for multidisciplinary fields, such as the field of soundsynthesis, which belong as a subcontext of more than one high-levelcontext. In link installation, context synonyms can provide what isanalogous in computer science as “multiple inheritance”, i.e., thedictionaries of multiple parents (“Music” and “Engineering” in thisexample) can optionally be included automatically in the formation ofthe aggregate dictionary for link installation, while only the one maincontext (“Sound Synthesis” in this example) has to be selected for linkinstallation.

To illustrate a “context synonym in FIG. 8, we could add a thirdsubcontext box under the “Top Level Context” box 180 entitled“Intermediate Context 3” which could have a different kind of border toindicate that it is a symbolic link to some other context. We could thendraw an arrow from the “Intermediate Context 3” box to its equivalent,such as either “Intermediate Context 1” 181 or “Intermediate Context 2”182.

FIG. 5 shows a display of two “competing definitions” for the phrase“Lagrange Interpolation” 151. Either of the two links 152 or 153 may beinstalled in a document containing the phrase “Lagrange Interpolation”.They are both named “Lagrange_Interpolation” because that happens to bethe title of both Web documents. However, the links point to twodifferent targets on the Web written by two different authors.

The “new” superscript after a link 152 or 153 means it was addedrelatively recently. In this example, both links for “LagrangeInterpolation” were added on the same day.

The “popular” superscipt for a link 152 or 153 means it has beenreceiving relatively frequent visits (or “hits”) via the W3K site. Thenumber of hits displayed in this case is 0.

Also displayed in FIG. 5 for each link 152 or 153 is the date 155 thelink was submitted, the number of hits 156 (number of times a anyone asclicked on the link at this site), a rating 157 for each link (which is0 since the links were just added), and the number of votes included ineach rating (also 0 at the moment). Available elsewhere on the websitealso is the number of times a link has been installed in Web documents.Finally, there are three links 154 for rating each link (assigning aquality score from 1 to 10 and optionally submitting a more detailedwritten review), reading the reviews written by others, and viewing allof the link's properties in tabular form. After the rating display is ahyperlink which a user can select in order to contribute a rating or areview of the link.

This completes a first-pass overview of the main pages and selectionsseen by the user while browsing the link databases. Functions availablewhile browsing will be described further in the following sections.

5.1.7 Adding or Modifying Definitions or Categories

In FIG. 5, the “Add a Definition” link 158 navigates to the form shownin FIG. 6 for adding another definition link for Lagrange Interpolation.The current key phrase “Lagrange Interpolation” is filled into the“Topic” field 161, and the context path leading to the key phrase isfilled into to “Context” field 160. This makes it convenient to enter anew source of information (definition) on a topic (key phrase) whilebrowsing.

When “Add a Category” or “Add a Key Phrase” is selected from thetop-level context (or “Add . . . ” is selected on the main website homepage), the “current context” field of the form becomes instead a pop-upHTML “select” list containing all of the contexts presently in thedatabase, making it convenient to quickly select any context in which anew subcontext or key-phrase is to be added.

The only required fields on the add-definition form (FIG. 5) are the URL162 and user's email address 169. All others are optional.

The URL is the new definition, and it is tested by the server to makesure it is responding. If the Site Title field 163 was left blank, thetitle of the Web page addressed by the URL, which is automaticallyretrieved by the server (using the Perl LWP module), is filled inautomatically as the link title.

The contributor's email address is required because all submissions tothe server in the preferred embodiment are associated with thecontributor's email address. However, there are alternative means foridentifying users known in the art, such as a more conventionalregistration procedure in which the user chooses a login name andpassword. The preferred embodiment ensures that the email address givenreally reaches the user. If the user is new, an authorization process,described in §5.1.9, is initiated which tests the user's email address.

While not required, the link contributor is invited to write a shortdescription 164 of the website, specify the minimum 165 and maximum 166educational level covered at the site (usually done by the author of thesite), and specify the type of resource 167 (home page, conferencepaper, book chapter, or the like). The user may also type in his or hername 168.

Fields such as educational level 165 that are potentially confusing tendto have a “Help” link 62 next to them. For example, the educationallevel help 62 explains that the numerical value is in units (loosely) of“years of education likely required to understand the material”. Aminimum level with no maximum level corresponds to setting one levelrather than a range of levels. When no educational level at all isprovided with the definition, the link server will attempt to compute itautomatically based on the level of the links it contains, as will bedescribed. In a script-based submission, finer control is possible usingadditional level-related properties.

Things like “educational level” and “resource type” are examples of linkproperties. The context path leading to a link is also one of itsproperties, as is its URL, title, description, and so on. A link canhave more properties than these, some of which will be described below.The “Specify Additional Properties” link 61 takes the user to a largerform where the additional properties can be specified.

When the user is satisfied with the filled in definition-submissionform, the submit button 60 can be pressed to send the form to the linkdatabase server (a computer at w3k.org in this case). At that point, theserver tests the URL by retrieving the first page, checks that theuser's email address is known and that the user's IP address and cookieinformation match information previously stored on the server (otherwiseauthorization is carried out), checks for duplication of the key phraseand URL in the given context, possibly checks the URL target for“inappropriate content”, assigns an automatic educational level if nonewas provided (unless automatic level assignment is already scheduled atregular intervals), and adds the new definition to the link database forthe current key phrase (and context path, if the database file holdslinks for multiple key-phrase contexts). If the addition was successful,the user is navigated to a dynamically generated Web page summarizingthe information added to the database. If there were any problems, anerror page is generated listing the reason(s) for failure to accept thepage.

A far quicker means of entering definitions is by means of dictionaryfile submission which can be regarded as a script-based replacement ofthe above browser-based interface. An example of such a dictionary fileis given in a later section. The form for submitting such a file may bereached via the “Submit Dictionary File” link in the standard menu, oras an option under the “Add to or Edit the W3K” option on the serverhome page.

5.1.8 Private Context Trees

As mentioned when describing the standard menu 130, known users mayoptionally create a new top-level context tree which is private to thatuser or to one or more groups identified by the user. This mode of usageis advantageous for private usage without incurring collisions withlinks in the main “global” context tree shown in FIG. 3. It is furtherthe only way a known user can submit large quantities of contexts, keyphrases, and links by means of a dictionary file submission, since thatoperation is not permitted in the global public context hierarchy.Further details will be described.

5.1.9 User Authorization

Whenever a user requests an operation on the server requiringinformation to be stored on the server (any “editing operation”), theuser must be “known.” Being known means the email address of the userhas been given by the user to the server, and the email address has beenverified by the server to work (reach the user). When an editingoperation of any kind is requested (including the simplest form of linksubmission, or even a link rating from 1 to 10), if the user is not yetknown, an “authorization process” is carried out as a preliminary stepin the desired editing operation.

In the authorization process, the user submits his or her email addressin a simple Web-page form, and the server (1) emails a randomlygenerated ASCII string to that email address, and (2) navigates the userto a Web page containing a form for receiving that random string fromthe user. The form also instructs the user to receive the email and topaste the random string into the second authorization form and submitit. This process verifies that the email address in fact reaches theuser.

The email address and IP address of the user are then saved on theserver. Additionally, the same information is written on the user'scomputer using a browser cookie. If the cookie goes away for any reason,or if the user later comes in from a different IP address for whichauthorization has never occurred (e.g., due receiving a new dynamicallyassigned IP address from an ISP, or using for the first time a differenthome computer connected directly to the Internet), authorization istriggered once again when any editing operation is requested. Userscoming in over dynamically assigned IP address generally have to beauthorized for each session until all such IP addresses have been seenand logged on the server along with the user's email address.

After a successful authorization, the user may use the “Back” button inhis or her Web browser to find the page which triggered theauthorization process, and resubmit the form successfully.

5.1.10 Link Properties

Many other properties can be specified for a link besides the URL 162and email address 169. One of the most important properties, brought outin the main form, is educational level 165. Both a minimum 165 andmaximum level 166 can be set. When the link-target document is writtenat a single well-defined educational level, such as “10^(th) grade”, themin and max can be set to the same value (such as 10), or the max can beleft unset (which defaults to level 100, meaning no maximum). When thedocument spans a wide range of educational levels, such as a welldesigned “topic home page” might do, the min and max can be setappropriately to cover the estimated range. The minimum level still setsthe official “level” used in automatic level assignment for otherdocuments, but the maximum level, if specified, may affect linkinstallation when a specific level range is specified for that. Aneducational level is implemented a floating-point number, so that alevel of 10.5 can be specified, e.g., in the form 165 or 166.

Another important link property, also on the main form, is resource type167. Resource types include dictionary definition, encyclopedia article,unpublished article, conference paper, talk overheads, refereed journalarticle, book chapter, book, tutorial, lecture notes, course readers,and the like. Sometimes authors may wish to screen out non-refereedsources such as conference papers or unpublished works. Of course,refereed publications and books will typically be hosted on the websiteof a publisher, requiring some form of payment for access, such as asite subscription or, preferably, a per-page “micropayment” such as thewell known Millicent system provides.

Additional optional properties may be specified on a second form byselecting the “Specify Additional Properties” link 61. Additionalproperties include source type (individual, educational institution,company, non-profit organization, etc.), geographical location, language(English is assumed by default), “viewer suitability” analogous to‘PG-13’, ‘R’, etc., for movies, a list of groups to be granted editingaccess, and so on.

Link properties added automatically by the server when installing a linkin a database include a unique integer ID, the email address and IPaddress of the link contributor, the date of submission, an initialrating of zero, an initial zero number of “hits”, an initial zero numberof “installs” in documents, and the like.

Link properties make it convenient to specify “virtual link databasedirectories” which include only the links satisfying certain criteriaspecifiable in terms of link properties. For example, a user may ask tosee only tutorials and books in a certain educational level range.Alternatively, an author may specify seeing only links belonging to thatauthor's email address, or group. Thus, properties enable selectivebrowsing (or listing) as well as more selective link installation. Suchselective browsing may be specified using the Search feature on the sitehome page 105, standard menu 130, or at the bottom of any Web page seenwhile browsing.

Link properties may also be usefully included in installed links (withinHTML “comments” or in specially defined XML tags) when indirect linksare being installed (that is, when the installed link points to acentralized link server which forwards the user's browser to theultimate destination). Installed link properties may be interpreted bythe link server to provide additional control over link behavior. Forexample, a teacher using Internet documents for a 9^(th) grade classcould configure the link server to suppress all links having aneducational level greater than 10. That way, when educational levelproperties are available for all links, as the present inventionprovides, documents may be populated with hyperlinks which can beconfigured not to refer a student to information at a more advancedlevel than the teacher desires. The teacher may further suppress anylinks with a viewer suitability rating below a certain value. Insummary, installed link properties enable dynamically configurable linkbehavior based on link property values.

In another use of installed link properties (which requires eitherbrowser support and/or local editing of the HTML containing theinstalled links), link properties can be associated with “classes” in“cascading style sheets” (an add-on to HTML) in order to display linksto dictionary definitions in one manner, encyclopedia articles inanother manner, and home pages in another, etc.

5.1.11 Restricted Directories

When a subcontext is created, it can be marked as “restricted” to theowner (creating user) or to groups specified by the owner. Restricting adirectory prevents anyone but the owner or specified groups frommodifying the subdirectory. The restricted directory can optionally bemade “invisible” to users other than those having modification rights,in which case the restricted directory is said to be “private”. Anunrestricted directory is said to be “public”. A restricted directorycan be deleted or renamed or otherwise reorganized no matter what itcontains. Typical uses of restricted directories include

-   -   Retaining the ability delete the entire directory and rebuild it        with a dictionary file submission.    -   Supporting a private dictionary corresponding to a particular        project, such as a book, in which it is desired to have complete        control over all links used in link installation.

The name of a restricted directory has the name of its first group (orowner, if no access groups are defined) automatically appended as asuffix to the name chosen by the owner in order to prevent conflictswith public directories and other restricted directories on the sametopic. With this convention, any number of users may have restrictedsubdirectories on the same topic. For example, in the subdirectory“/Music/Computer_Music/Synthesis/” there could beCommuted_Synthesis_by_mak@vipunen.hut.fi/Commuted_Synthesis_by_jos@ccrma.stanford.edu/

In this way, any number of experts may provide their own “packages” oflinks on the same topic.

A known user may even create a new top-level hierarchy which may bedesignated public, restricted, or private. User- or group-ownedhierarchies of this nature which lie outside the primary publichierarchy may be placed in a special standard menu item entitled“Alternate Universes”, e.g., to indicate that they are not a part of theprimary public context hierarchy.

5.1.12 Link Ratings and Reviews

When browsing reaches a key-phrase directory, as shown in FIG. 5,following each competing definition 152 or 153 is the hyperlink “RateIt” which navigates to a form where that definition (link) can be ratedon a scale from 1 to 10, and/or a written review about that link can besubmitted. If the user is not known, an attempt to submit a rating orreview routes the user to the authorization page, and after a successfulauthorization, the rating or review is accepted by the server.

All ratings and reviews are stored on the server along with the emailaddress (and IP address) of the contributor. Only one rating and revieware allowed per item per email address, but the user owning the ratingor review can modify either at any time. Certain “trusted” users, suchas website editors or expert consultants enlisted to help with ratingsand reviews, may be given higher weighting in the ratings, and thereviews may be organized by editors according to their quality.Otherwise, the rating system is straightforward and similar infunctionality to the five-star rating and review system used at<<http://www.amazon.com>> for books.

5.1.13 Link Installation

A primary function of the invention is to facilitate the installation ofhyperlinks in documents intended for the World Wide Web. This sectionprovides a detailed description of link installation in the preferredembodiment.

Installed-Link Types

There are at least four alternative ways to install a link in adocument.

In the first mode, a hypertext link is installed directly to thetop-ranked source of information on the topic identified by the matchingkey phrase in the user's submitted text. This is the first choicepresented in the “Link Type” radio-button-group 177 of the default linkinstallation form (FIG. 7). A disadvantage of this approach is thatlinks often become “stale” due to changing ISPs, changing filenames,etc., requiring the links to be re-installed from time to time. (Thelink installation server preferably tests all links in its databasesperiodically and eliminates them if they are unavailable for a prolongedperiod of time such as more than a week. When all links containing a badURL are automatically removed from the databases, all owners of thelinks are notified automatically by email and invited to submit anupdated version of the link(s).)

The second approach is to install an indirect link which links via acentralized server (such as a website providing the link installationservice). This choice is provided by the second radio button in the“Link Type” portion 177 of the default link installation form. Such anintermediate website acts as a so-called “proxy server” for the link.Indirect links may always point to the most up-to-date, top-rankedsource of information on any given topic. An example URL syntax for thismode of operation is<<http://www.w3k.org/jump.cgi?ID=35>>where it is assumed that each link has a unique integer identifier onthe proxy server, and jump.cgi is a CGI script which is passed theidentifier as if it were a form submission in which the form contained afield named “ID” with the value 35. To avoid having to assign uniqueidentifiers across all contexts, the context path can be included in theURL, e.g.,<<http://www.w3k.org/jump.cgi?ID=3&PATH=Engineering+Signal_Processing>>

Context paths can similarly be assigned integer IDs in order to shortenindirect URLs.

A third approach is to insert a link to the “key-phrase page” itself atthe centralized server (the page on the server listing all “competingdefinitions” for that key phrase). This is the third and final choice inthe “Link Type” radio group 177. In this case, an end user followingsuch an installed link will see all competing definitions, in rankedorder, instead of only one. The end user can then request that thedefinitions be reorganized according to various criteria such aseducational level, document size, type of resource (article, book,etc.), type of source (.edu, org, .com, etc., individuals, etc.), and soon, by making requests of the server interactively, or by means ofpreferences registered with the server.

A refinement of the third approach is to build or generate a morehelpful “key-phrase home page” on the link server. This page couldprovide, for example, a brief definition, followed by an organizedpresentation of all available sources of information, organized by typeand ranked according to quality in each case. In this format, the casualuser may be satisfied with a mere dictionary-style definition, while theserious scholar can more readily pursue a wider variety of sourcesbeyond merely the top-ranked source. Providing interactivereorganization of the definition page according to end user preferencesis preferable in this case as well.

A fourth approach is to use JavaScript features to install a snapshot ofthe key-phrase home page at the time of link installation. In thisapproach, a JavaScript pop-up menu may hold a list of all competinglinks for the linked topic.

Example Key-Phrase Home Page Format

Below is an example of how a very simple “key-phrase home page” might belaid out:

TABLE 1 Key Phrase: Dictionary-style definition Link to highest-ratedonline encyclopedia-style article Link to highest-rated online tutorial,if available Link to highest-rated textbook covering this topic, if anyLink to educational resources (online courses, degree programs, etc.)Highest rated related links (“See also” type information) Rank-orderedlist of encyclopedia-style links Rank-ordered list of online tutorialsRank-ordered list of other online information Rank-ordered list ofcontributed links of unknown type . . . Last unrated contributed link ofunknown type

The link database server preferably provides periodic link testing,average ratings computation, link reordering, automatic educationallevel assignment, and so on. It is also straightforward for the serverto format the key-phrase home page dynamically according to userpreferences based on link properties and other criteria. For fullgenerality, it is desirable to customize and differentiate key-phrasehome pages on the basis of language, educational level, and otherproperties. (They are already segregated according to context by thecontext hierarchy in which they reside.) To address the potentialenormity of this task, a mechanism for allowing known and trusted usersto submit key-phrase home pages for installation on the server can beprovided. For this purpose, the server can provide a template documentcontaining variables that are filled in by the server, in a manner oftenfound in website construction tools.

Link Color

While copious linking makes a set of documents very convenient tonavigate among, the high density of links can be distracting to the eye.For this reason, the link installation submission form provides acheckbox for requesting that the hypertext links be set to the samecolor as the surrounding text. This leaves only an underline to indicateeach link. Presumably, future versions of HTML and browsers will allowfiner control over the display modes of links, and it may in some casesbe possible to offer turning off all visual indications that a link is alink. This is because when links are installed at very high density,such as this invention makes possible, the reader can assume thatessentially all nontrivial words are linked. Links become the rulerather than the exception for all “uncommon” words in a document.

Avoiding Links Altogether

In an alternate mode of usage, any word or phrase can be selected intext displayed by the user's browser and “looked up” at a server websitecontaining the link databases. A similar mechanism is currentlyavailable in Microsoft Internet Explorer 5: The right-click menucontains an entry “See more with Lycos!” which, when selected, causesthe selected phrase (or word last clicked with the mouse) to be lookedup in the search engine at the Lycos website (http://www.lycos.com).

In the case of the present invention, in which the database server mayact in place of the Lycos website, if the word or phrase is found in thelink database, the user may be taken to the page of “competingdefinitions” (all links) for that topic. If the topic is available inmultiple contexts, a list of all distinct contexts can be firstdisplayed, so that the user can select which one he or she had in mind,and then be taken to the definition page in the selected context. If theterm is not in the link database but coincides with a context directoryname, that directory can be displayed by the browser. As a lastalternative, the unrecognized phrase may be forwarded to an ordinaryonline dictionary (for single words), encyclopedia, or Internet searchengine. The link-free lookup mode described in the previous paragraphscan be supported in any number of applications, not just Web browsers.For example, the word processor Microsoft Word already supports lookingup an ordinary dictionary definition of a word by selecting the word andchoosing the “Define” item in the right-click pop-up menu. Another itemin that menu could be “Look it up at the W3K”, for example. A link-freelook-up service of this nature could be provided in any applicationwhich displays text and supports text selection by the end user. Theservice can be provided either over an Internet connection as describedabove, or, in the absence of an Internet connection (or supplementary toit), using the single-computer embodiment of the present inventiondescribed in §5.2.

In the preferred embodiment, end users of the link-free lookup servicemay optionally register with the database server in order to specifypreferences such as whether a key-phrase lookup (sans link) shouldnavigate to the key-phrase home page or more directly to the currentlyhighest ranked definition for that key phrase. The user may also informthe server of his or her educational level, desired viewer suitabilityrange, and the like.

To support link-free lookup mode, the database server may accept a URLcontaining a “virtual form submission” of a link-free lookup form. As asimple example, a lookup request for the phrase “Hubble constant” couldbe sent to the database server by “navigating” to the URL<<http://www.w3k.org/linkfreelookup.cgi?TEXT=Hubble+constant>>

The CGI script linkfreelookup.cgi runs and may immediately issue a“navigation” output to the highest ranked link matching “Hubbleconstant”, if any. The URL may also include a user name. If userpreferences exist, the script may alternatively navigate to a key-phrasepage of competing definitions for the Hubble constant, and so on.Additionally, any number link properties may be specified in the URL aswell.

Link Installation Form Operation

FIG. 7 shows the default web page for submitting documents to havehypertext links installed by the server. The user pastes text to be“linkified” directly into the “Text or URL” textfield 170. In thisexample, a URL 77 has been specified, indicating that an entire websiteis being submitted for link installation, as will be described furtherbelow.

Three input submission formats may be specified by the “Input”radio-button group 171: HTML, Plain ASCII, and LaTeX source. Inaddition, there is a “Help” link 174 which navigates the user todocumentation on the relevant considerations for each choice.

In the example of FIG. 7, submission of HTML format is selected in theinput-format radio group 171. In the case of “plain ASCII” submission,the output is also normally received in HTML format; this facilitatesfast construction of Web pages from simple ASCII text files. It also canbe used to quickly obtain a browsable Web directory from a list ofkeywords generated by other means. Since some HTML editors support “dragand drop” link installation from another document, an automaticallygenerated list of HTML links can be very useful even for manual linkentry in an HTML editor.

In the case of LaTeX source format, links are installed in the form ofan invocation of the macro \htmladdnormallink{text}{target}, which isdefined in the widely used html.sty LaTeX style file.

When the input format is HTML, it is parsed to prevent accidentalreplacement of HTML tag data with links. In particular, it is importantnot to install links within the anchor text of existing links. HTMLparsing can be accomplished using the HTML Perl package (see, forexample, page 716 of the Perl Cookbook by T. Christiansen and N.Torkington, O'Reilly, 1998).

In a similar manner, LaTeX directives are avoided in the text matchingalgorithm within LaTeX source. (Perl for LaTeX parsing is available inthe latex2html Perl script, freely available athttp://ctan.tug.org/ctan/.)

Linking is preferably suppressed when the recognized phrase coincidesthe name of the current section or document, i.e., a phrase that resultsin a link to the current page.

When “Link only the first occurrence . . . ” is selected in the firsthalf 175 “Occurrences” section of the link-installation submission form(FIG. 7), only the first occurrence of the phrase is linked each page(HTML) or section (LaTeX). Otherwise all occurrences are linked.

A second pair of radio buttons 176 exists for specifying that links beinstalled for either all emphasized words or phrases, or only emphasizedwords or phrases. Emphasized occurrences may appears as “\emph{. . . }”in LaTeX and as <I>.</I> or <B>. . . </B> in HTML.

The two radio-button-pairs 175 and 176 can be considered to specify “twobits” which select among the following cases:

TABLE 2 00 link all occurrence of a key phrase, whether emphasized ornot; 01 link all occurrences of a key phrase, but only when emphasized;10 link the first occurrence of a key phrase in each page (whetheremphasized or not), and all emphasized occurrences; and 11 link only thefirst emphasized occurrence of a key phrase.

As a further special case, any URLs found as plain text in the sourceare by default converted to links that display their own URLs as anchortext. Many email programs and word processors presently perform thistransformation on URLs detected as plain text in received email.

The “Link Type” radio button group 177 selects among three of the basicinstalled link types discussed in the first subsection of this section.

The “Link Color” select pop-up list 178 provides for link colorselection as discussed above. In addition to the standard color names,there is a “take default” selection which does not specify the linkcolor, thereby leaving it to the HTML cascading style sheet or user'sbrowser to choose link color.

The “Contexts” radio group 179 provides some high-level choices ofcontext selection for link installation. The first choice, “All W3Kcontexts” corresponds to combining all context dictionaries in theentire context hierarchy. As the context hierarchy grows, this canbecome a computationally expensive option, even when the aggregatedictionary is maintained as an existing file at all times. When a“current context” exists (as result of browsing or user preferences), itand its extensions are preferably listed first in the aggregatedictionary, as will be clarified further below.

The second radio button in the “Contexts” radio group 179 selects onlythe “current context” (/Music/Computer_Music). The current context isnormally established by browsing or by standing user preferences. (When“Install Links” is selected in the standard menu 130 while browsing, thelast context displayed in the browser becomes the default currentcontext.) A browser cookie is preferably used to remember the mostrecent “current context” for each user across sessions.

Installing links from only the current context is not as narrow as itmay seem at first since normally the context dictionaries for /Music and‘/’ (the top-level generic dictionary) are included, as well as allsubcontexts of Computer_Music. The two “Extensions” checkboxes 70provide all-or-nothing control over appending parent and subcontextdictionaries to the current-context dictionary. Additionally, if thesubcontext /Music/Computer_Music/Sound_Synthesis is a synonym for/Engineering/Signal_Processing/Sound_Synthesis, say, and if “multipleinheritance” is enabled at all subcontext hierarchy levels (an advancedlink installation option), then the context dictionary for all of SignalProcessing and /Engineering would be folded in, at a lower precedencelevel, of course, since they are listed after all subcontexts of /Music.In summary, the aggregate dictionary list built for link installation bythe server can be rather large even when only the current context isselected for link installation.

The third and final option in the “Contexts” radio group 179 is toprovide an explicit list of context dictionaries. A list of contextdictionaries can be accumulated via browsing in the manner describedabove, or a list can be submitted dictionary-file format. Additional“virtual context dictionaries” may be defined by means of the Searchfunction, with the search results forming a link subset which can beassigned a name and treated as a dictionary. It is preferable to offerconvenient hierarchical browsing of the selected portion of contexthierarchy represented by the dictionary list. Any search result may alsobe displayed as a dictionary file. Dictionary files are discussed moredetail below.

Dictionary lists may be stored on the server in a directory devoted toeach user or in a file with user's email address forming part of thefilename, as shown in the example of FIG. 7. They may also be stored onthe user's computer via browser cookies.

The “Min Level” 71 and “Max Level” 72 pop-up lists allow specificationof a range of educational levels for link installation.

While any number of properties may be associated with links, thetop-level default submission form of FIG. 7 for link installationinvites link selection according to only a few properties such ascontext 179 (determined by dictionary selections) and educational level71,72. Installation specifications based on additional properties may beobtained by following the “Specify Additional Properties” link 174 andfilling out a larger form allowing specification according to morecriteria, using well known principles of database subset selectionaccording record properties.

When the user presses the “Submit” button 173 (or the submit button of along-form submission form), the server receives the filled-out formspecifying how links are to be installed, processes the submitted textin a CGI Perl script or other server-side software to install the links,and generates output consisting of the user's submitted text with allthe new links embedded.

Link Installation on the Server

Actual link installation from an aggregate dictionary by the server,while one of the more complex and resource-demanding operations, isbased on well known database technology and methods in computer sciencefor string search and replacement. The Perl language is well suited forthis task.

In the preferred embodiment, an aggregate dictionary file is prepared onthe server based on the user's link-installation specifications and thecurrent contents of the server's link database. This dictionary file isthen “applied” to the user's submitted documents in order to replace keyphrases by hypertext links. A Perl script illustrating link installationfor HTML files is included in Appendix A.

The preferable details of the methods used depend on the relative sizesof the files involved. For example, if stringent conditions arespecified on link properties for installation, and if a large file issubmitted from the user, it may be the case that the aggregate linkdictionary is much smaller than the combined size of the files submittedfor link installation. In this case, it may be fastest to search thesubmitted file for each link in the aggregate dictionary.

If, on the other hand, the number of eligible links is large (e.g., “AllW3K contexts” was selected in the Contexts section 179 of the linkinstallation form), and if the submission itself is small, it may bepreferable to search the aggregate dictionary file for each possible keyphrase in the input file using well known “incremental search”techniques.

In either case, if the user has specified that only emphasized words orphrases are to be linked, then all phrase boundaries are known, and thiscan be used to greatly reduce the computational burden of thestring-matching task.

Single-Page Submission

For single-page text submitted using the HTML form of FIG. 7, the outputHTML may be returned to the user in the form of a “dynamic Web page.”That is, the user's browser immediately “navigates” to the automaticallygenerated HTML page as if it were already somewhere on the Web. At thatpoint, the user can select “Save As” in the Web browser in order to savethe HTML in a local file, or “View Source” can be selected in thebrowser to enable copy/pasting of the generated HTML into a text editorfor further editing.

Submission of an Entire Website

In an alternative mode of submission, shown in FIG. 7, the userspecifies a URL pointing to the submitted document in place of the textof the submission itself. This mode of submission is more convenient forlinking entire websites. In a typical configuration, the serverprocesses the submitted file and all files reachable from the first viahyperlinks, provided that the reachable files reside somewhere on thesame website (as defined by its URL). In other words, links are followedprovided the first portion of the URL matches that of the submitted URLin its entirety.

In the case of URL submission, the processed document is not returned asdynamic HTML, but rather as a hyperlink to a single binary output fileon the server containing all the processed files. This output file maybe created by combining all processed files into one using the freelyavailable tar program, and further compressed using the freely availablegzip program. The tar and gzip programs are available from the GNU FreeSoftware Foundation (http://www.gnu.org/). The output file can then be“downloaded” to the client computer by clicking on the hyperlinkpointing to the output file in the dynamically generated HTML. The userthen unpacks the file on his or her local computer using, e.g., gunzipand tar, or the shareware program WinZip. As a third alternative,preferred for large submissions or over slow internet connections, theuser may specify the URL of a single composite file in “tarred andcompressed” format, i.e., created using gnutar and gzip in the same waythat the server's output is prepared in the case of multi-filesubmissions.

The filename extension is used by the link installation server todistinguish between pointers to websites (.html or no extension,indicating a directory) and compressed tar files (.tgz or .tar.gz). Ifthe text appearing in the “Text or URL” textfield of thelink-installation submission form starts with “http:”, “ftp:”, or“gopher:”, a URL is assumed.

The following sections will describe further details of the operationsindicated above.

5.1.14 Dictionary Search Order

Link installation usually occurs within a “current context” or a list ofcontexts. In the example described above, the current context may be setaccording to the location of the browser when “Install Links” wasselected by the user. Alternatively, one or more contexts may be setexplicitly in a dictionary list provided by the user when filling in thelink installation form of FIG. 7.

In the simplest mode, the current context dictionary is searched firstfor matches in the user-supplied text, and matches are transformed intolinks. The process is “idempotent” since matches will not occur withinthe link syntax itself (such as in HTML anchor specifications or LaTeXmacro arguments). As a result, dictionary entries are ordered fromlongest to shortest phrasings, as discussed above.

As described above, the dictionary for the current context is optionallyaugmented by the union of all lower-level dictionaries within thatcontext. Current-level definitions take precedence over lower-leveldefinitions in any key-phrase collisions. Collisions among lower leveldictionaries are not explicitly arbitrated (since that could beaccomplished by listing them explicitly), so that the first occurrenceof a lower-level definition will take precedence (when not defined atthe main level). This follows simply from the convention that “the firstmatch wins”.

The purpose of adding in all lower level directories is to provide areasonably complete dictionary at a high-level node without having toduplicate definitions from lower-level contexts. In principle, suchduplication could be avoided by moving all lower-level definitions tothe highest possible context. As a simple example, the term “idempotent”is a math term used in many technical fields, and it is not anEnglish-language term (according to the Funk & Wagnalls Standard DeskDictionary). Therefore, “idempotent” can be defined without conflict inthe top-level dictionary for the English language. In practice, however,it works out better to define terms in their “most natural” subcontext,and let their definitions “float up” as far as they can go withoutcollision. Positioning a term within its “most appropriate” contextmakes the hierarchical dictionary better organized and instructive whenbrowsing.

When an undesired definition is encountered, it can be “fixed” (thefirst time) by defining the term in the current context, since that willtake precedence over all subcontexts and parent contexts. A conflictcannot occur in the current context (in principle) because a context isby definition a name space in which every term has a unique definition.Another solution is to list a specific ordering of lower-leveldictionaries so that the first match is the desired one. After thecurrent-level dictionary is “applied”, including all subcontexts, theparent node is normally next in the aggregate dictionary. It is searchedfor further matches, so that more general terms in the higher contextnot “overridden” by the lower contexts will be linked to theirdefinitions. This process continues until the top-level context node isreached in the aggregate dictionary.

Note that it is not necessary to create an explicit aggregatedictionary. It is equivalent to instead apply context dictionariessequentially in the proper order.

As mentioned above, a list of context dictionaries may be specifiedexplicitly in a variety of ways. This is analogous to specifyingmultiple libraries when linking a computer program. The order ofspecification is important since the first match is taken. This featuremay be used by specifying ancillary fields after the main field of theauthor. For example, a physics professor might include certain mathcontexts after the appropriate context(s) within the field of physics.

5.1.15 Maximizing Match Length in Key Phrase String Matching

As discussed above, there may be several forms of a key phrase(“synonyms”) corresponding to the same URL. It is normally preferable tomatch the longest form present in the text so as to avoid multiplegeneric matches such asTaylor Series Expansionwhen there exists a longer matchTaylor Series Expansionhaving a completely different meaning. Maximal-length matching isimplemented in the preferred embodiment by maintaining the key phrasesin order of longest to shortest and then traversing the dictionary inthe prescribed order.5.1.16 Contributing Links

Link Submission Support on the Server

-   -   enables all users to assist in the expansion of the “knowledge        tree” represented by the link database dictionaries, and    -   enables individual users to augment the link installation system        to meet their special needs.

For example, a known user can contribute his or her own link database,select only it for search during link installation, and thereby obtainfull control over the links which may be installed.

A personal link database can be very useful to the author of a booktypeset in LaTeX, for example. Since LaTeX supports the generation of anindex file, and since the freely available latex2html Perl script willconvert a book index into an HTML page, such an index can be easily andautomatically be converted (e.g., in the Emacs text editor) to adictionary file format acceptable by the server. The entire book canthen be processed by the server to install links pointing somewhere intothe book for every occurrence of an indexed word in the book. Otherlinks can of course also be included.

Another application of LaTeX index files is to merge the indexes ofrelated books in order to generate a link database for a particular“field,” spanning a specific set of resources.

Only known users can submit links and/or create subcontexts or keyphrases. All submissions are “owned” by the submitting email address orgroups defined by the submitting user. (Email addresses are verified bythe authorization process described earlier.) Only the owner, groupmember, or server webmaster may make changes in submissions (except fortheir ratings and reviews, of course, which any known user can affect).

Since any number of users may be trying to submit link databasessimultaneously, one of many known schemes for “file locking” is neededfor the database files and directories during a submission. To avoidperiods of database unavailability, submitted public databases can befirst prepared in a temporary directory and extensively checked forcorrectness by the server, including owner checking, name-collisionchecking, URL validations, format checks, and so on. During thisprocess, the eventual destination directory is preferably write-locked.Since final installation may be carried out by rapidly renaming the twodirectories, downtime for read access is minimized. Implementing linkdatabases as many files distributed throughout a context directory treemakes database updates simpler, since updates in one context need notaffect activities going on in other contexts.

5.1.17 Dictionary File Format

A link database (or dictionary list) may be submitted in a documentedASCII format supported by the server. Since all properties are optional,the submitted file can be as simple as a list of key phrases and theircorresponding URLs. Below is a “dictionary file” which can be used toinitialize a context hierarchy for the examples seen in the FIGS. 3-5:

-   GROUPS=CM_DSP-   PATH=/Education/Technology-   KEY=W3K-   URL=<<http://www.w3k.org>>-   #--------------------------------------------   KEY=/Legal/GNU General Public License-   URL=<<http://www.fsf.org/copyleft/gpl.html>>-   #--------------------------------------------   PATH=/Music/Computer_Music/Signal_Processing/People-   KEY=Julius 0. Smith III |Julius 0. Smith|Julius Smith-   URL=<<http://www-ccrma.stanford.edu/˜jos/>>-   KEY=JOS-   URL=<<http://www-ccrma.stanford.edu/˜jos/>>-   #--------------------------------------------   PATH=/Music/Computer_Music/Centers/CCRMA-   KEY=CCRMA Courses-   URL=<<http://www-ccrma.stanford.edu/CCRMA/Overview/courses.html>>-   KEY=CCRMA Research-   URL=<<http://www-ccrma.stanford.edu/CCRMA/Overview/research.html>>-   KEY=CCRMA Overview-   URL=<<http://www-ccrma.stanford.edu/CCRMA/Overview/Overview.html>>-   KEY=CCRMA-   URL=<<http://www-ccrma.stanford.edu/>>-   #--------------------------------------------   PATH=/Music/Computer_Music/Sound_Synthesis-   SYNM=/Engineering/Signal_Processing/Sound_Synthesis-   KEY=Lagrange Interpolation-   URL=<<http://www-ccrma.stanford.edu/˜jos/Lagrange_Interpolation.html>>-   LEVEL=12-   KEY=Lagrange Interpolation-   URL=<<http://www.acoustics.hut.fi/˜vpv/publications/vesa_phd.html>>-   KEY=Digital Waveguide Synthesis-   URL=<<http://www-ccrma.stanford.edu/˜jos/wg.html>>-   KEY=Commuted Synthesis-   URL=<<http://www-ccrma.stanford.edu/˜jos/book2000/CommutedSynth.html>>-   KEY=Virtual Analog Synthesis-   URL=<<http://www-ccrma.stanford.edu/˜jos/VirtualAnalog/VirtualAnalog.html>>-   KEY=Physical Modeling Synthesis-   URL=<<http://www-ccrma.stanford.edu/˜jos/pmupd/PMSynthesis.html>>-   #--------------------------------------------   PATH=Music/Computer_Music/Signal_Processing/Sound_Synthesis/Vintage_Methods-   KEY=Additive Synthesis-   URL=<<http://www-ccrma.stanford.edu/˜jos/SMS_PVC/AdditiveSynth.html>>-   KEY=Sampling Synthesis-   URL=<<http://www-ccrma.stanford.edu/˜jos/samplingsynth.html>>-   KEY=Cross-Synthesis-   URL=<<http://www-ccrma.stanford.edu/˜jos/crosssynth.html>>-   #--------------------------------------------   PATH=-   Music/Computer_Music/Signal_Processing/Sound_Synthesis/Acoustic_Instruments-   KEY=Bowed String Synthesis-   URL=<<http://www-ccrma.stanford.edu/˜jos/book2000/Bowed_Strings.html>>-   KEY=Brass Synthesis-   URL=<<http://www-ccrma.stanford.edu/˜jos/pmupd/Brasses.html>>

Several features of the ASCII dictionary format may be noted:

-   -   The GROUP directive lists the names of all groups which share        ownership the submitted links. In this example, only one group,        CM_DSP, is specified. Group specification is optional.    -   The PATH directive sets the default context for subsequent        entries.    -   Anything after ‘#’ is interpreted as a “comment” and ignored.    -   An entry can override the default path by including its own        “absolute path” specification, as illustrated by the entry for        the “GNU General Public License”.    -   Path components are separated by ‘/’ as is conventional in UNIX        file systems. Spaces before and after a ‘/’ are removed by the        interpreter, and spaces within KEYs are converted to ‘_’. (Any        number of adjacent “whitespace characters” are converted to a        single ‘_’.)    -   The SYNM directive declares a synonym for the current default        context. In this example, /Music/Computer_Music/Sound_Synthesis        is declared to be synonymous with        /Engineering/Signal_Processing/Sound_Synthesis.    -   KEY synonyms may be declared in a single entry by separating        them with vertical bars ‘|’.    -   KEY synonyms may also be created by specifying the same URL in        two different entries (as in the JOS entry).    -   Order is important: The phrases “CCRMA Overview” and “CCRMA        Research” will be transformed into links before the word        “CCRMA”, as a result of the ordering shown.    -   The only example of “competing definitions” in this dictionary        is the case of “Lagrange Interpolation”.    -   The first entry for “Lagrange Interpolation” is accompanied by        an education level range specification using the LEVEL        directive. It is set to 12 indicating that a high-school senior        (at least one on the “math track”) should be able to fully        understand the main thrust of it. Alternatively, a minimum and        maximum educational level could have been specified using the        MIN_LEVEL and MAX_LEVEL directives. The arbitrarily set maximum        value of 100 means “no maximum”. Level ranges are more        appropriate for “home pages” and the like which link to a        variety of documents at a variety of educational levels.

Only trusted users can submit links and contexts wholesale in thismanner to the link database server. However, any known user can submitsuch a set of links to a restricted or private directory. Otherwise,known users are allowed to submit one link at a time using the “Add aResource” submission form described earlier.

If there are any pre-existing links in the same context directory withthe same name and URL as a newly submitted link, the pre-existing linkis retained unless the new submission is by the same owner. (Linkproperties could be updated or added in this manner, for example.Ratings and reviews are not affected since they may not be submitted ina dictionary file.) Rejected submissions are listed in a message fromthe server delivered in a dynamic web page, as is typical. Similaraction is taken for other kinds of messages to the user as needed.

If the specified context directory does not exist, it is created, andthe email address of the creating user is logged as its owner. Theserver automatically installs an encoding of the owner's email addressin each link entry by means of an additional link property. Otherproperties, such as initial ratings, date-of-submission, etc., areinstalled by the server. Only the owner or group-member or serverwebmaster may modify an existing link or directory.

Similar submission protocols can perform editing operations which wouldotherwise be laborious over the browser-based user interface describedabove, such as deleting a database subdirectory and all its contents(provided, of course, that everything to be deleted is owned by theperson or group making the request). For example, the directives

DELETE_LINK /Physics/Quantum_Mechanics/Planck's_Constant DELETE_PATH/Physics/Quantum_Mechanics/ Schroedinger's_Wave_Equation/can be used in place of online interactive editing of the server linkdatabase. In general, there is preferably a script-style equivalent forall operations performable interactively via a graphical user interfacesuch as Web browsers provide. In addition to performing the operationsmore quickly and conveniently, script-style alternative interfaces arevery important for the visually impaired. Scripting also provides ameans of conveniently resubmitting all links contributed by the user,thereby making it convenient for users to maintain “back-ups” of theirsubmissions in a form that can be easily restored on thelink-installation server. Browsing and Search features can be used toobtain a dictionary-file display of all links owned by the user.

There may be a limit placed on the number of database links andsubdirectories that can be submitted by any one user (email address) orgroup. This is to guard against accidents, malicious “hacking,” and tofacilitate editorial tracking of contributed content. A certain amountof automatic checking for inappropriate content is possible, based onsearching link targets for inappropriate words. Users can apply for“trusted” status by sending email to the server webmaster or otherauthorized agent. Trusted users may be given a higher contribution limitand perhaps also a higher weighting in link ratings. A group of userscan be formed in which each member is trusted within that group.

5.1.18 Use of Dictionary File Format to Specify Context Lists andDictionary Lists

When specifying a list of context dictionaries for link installation, itis convenient to be able to use dictionary file format. When used inthis way, all PATH directives in the file are extracted to form a listof contexts. If any links are specified for a particular context PATH,then only those links will be eligible for installation. Additionaldirectives are provided which correspond to the options available forcontext dictionary specification, such as include parents, includesubcontexts, and allow multiple inheritance. For convenience, theseaggregate-dictionary-building directives are ignored when submitting adictionary file as a means of submitting links.

Using the previous example dictionary file now to specify an aggregatedictionary for link installation gives results equivalent to thefollowing dictionary file:

-   -   GROUPS=CM_DSP # Only operative if selecting based on group    -   PATH=/Education/Technology    -   PATH=/Music/Computer_Music/Signal_Processing/People    -   PATH=/Music/Computer_Music/Centers/CCRMA    -   PATH=/Music/Computer_Music/Sound_Synthesis    -   SYNM=/Engineering/Signal_Processing/Sound_Synthesis    -   PATH=Music/Computer_Music/Signal_Processing/Sound_Synthesis/Vintage_Methods    -   PATH=Music/Computer_Music/Signal_Processing/Sound_Synthesis/Acoustic_Instruments        Adding some typical directives and eliminating some redundant        specification leads to    -   GROUPS=CM_DSP # Only operative if selecting based on group    -   PATH=/Music/Computer Music MULTIPLE_INHERITANCE_DEPTH=2    -   OWNERS_ONLY    -   MIN_LEVEL=12    -   MAX_LEVEL=100    -   SUITABILITY=PG-13 # Movie and V-chip names understood    -   SOURCE=ALL    -   TYPE=Refereed    -   PATH=/Education/Technology

Several features of this aggregate-dictionary specification may benoted:

-   -   MULTIPLE_INHERITANCE_DEPTH=1 means that the context dictionaries        of linked parents are appended to the aggregate dictionary for        context synonyms occurring 1 level below the current context or        less. This is just sufficient to pick up the “engineering        parents” of context Sound_Synthesis without also including        linked parents of lower levels.    -   The OWNERS_ONLY directive restricts the aggregate dictionary to        links owned by members of group CM_DSP.    -   The minimum and maximum educational level restrict link        installation to links rated at 12^(th) grade or higher.    -   Source “ALL” means any source. Other choices include EDUCATIONAL        (.edu), COMMERCIAL (.com), and so on. As usual, multiple sources        can be separated by vertical bar ‘|’.    -   The TYPE is resource type. “Refereed” is a symbol for all        refereed source types (journal article, book, etc.) If no type        was specified by the contributor, it is UNKNOWN.    -   Order is important: The listed contexts will be appended in the        order given, with the first one listed being considered the        “current context”.    -   Dictionary combining directives as shown in this example are        “sticky”, meaning that they apply also to subsequently listed        context paths unless they are explicitly reset, or set to “NIL”        indicating no value (to obtain the system default behavior).        5.1.19 Security Considerations

The IP address is stored as well as the verified email address forsecurity reasons. A user with “root privileges” on a personal machinecan generate any number of return email addresses, while the number ofIP addresses available to an individual is usually very limited. Forexample, if unusually many email addresses are found to belong the sameIP address, a warning can be automatically emailed to the webmaster whocan look into the matter further, such as by inspecting allcontributions from that IP address. If an IP address turns out to belongto a malicious “hacker”, it is straightforward using standard UNIX toolsto eliminate all database entries and directories associated with thatIP address, barring it from further contributions, and so on. When theIP address is dynamic, as is often the case when a commercial InternetService Provider (ISP) hosts the user's account, it is less likely thatmany different email addresses will belong to the same person, and theISP can be contacted for assistance. Note that it is very easy toarbitrarily set the “From:” field in any email message; therefore, the“Received” fields in received email may be analyzed by the server to getcloser to the true originating location. In Netscape Navigator, forexample, select “View/Headers/All” to see such fields in received email.

5.1.20 Link Database Implementation

Each link database may be implemented on the server as a plain ASCIIfile in a directory structure that corresponds to the hierarchicalorganization of the link databases.

The complete hierarchy can also be implemented in a single file whichcontains path information for each link entry. The initial prototype ofthe present invention used a single link database file based on thelinks-2.0 software scripts from Gossamer Threads, Inc.(<<http://www.gossamerthreads.com/scripts/links/>>). In thisimplementation, the context path information is included in what iscalled a “link category”. In adapting the links-2.0 scripts, categorieshaving no subcategories are considered to be “key phrases”, and actuallinks within a key-phrase (bottom-level category) are treated as“competing definitions”.

For a variety of reasons, use of a single links database file is notconsidered the best mode of carrying out the present invention. Instead,a hierarchical file system implementation is preferred in which thedirectory path corresponds to the context, and the database file in acontext directory contains only links for that context (along withperhaps a limited number of subcontexts).

Alternatively, an evolutionary path can be followed starting out with asingle database file, followed by splitting into separate database filesfor top-level contexts, followed by further splits as the files grow toolarge, etc. (The links-2.0 system advises a limit of 10,000 links forits one-file link database system managed by Perl CGI scripts.) On eachsplit, the first path component stored in the link database may beremoved since it becomes implied by the directory in which the databasefile resides.

A database directory may contain both files and directories.Subdirectories are interpreted as subtopics, and the hypertext links forthe current directory (when it is a key-phrase directory) may residewithin a single ASCII file named “links.txt”, for example, preferablylocated in a context directory containing the key phrase. The links.txtfile contains a list of hypertext links for the current context in aplain ASCII format described below.

There may be a temporary “system file” for each active user which listscurrent selections and other state information pertaining to that user.Multiple selection configurations may be stored on client computers bymeans of the “cookie” mechanism supported by the major Web browsers. Thename of a user's configuration file may include the user's emailaddress, if known, and otherwise an arbitrarily assigned session ID for“unknown” users. All active sessions preferably time out after a periodof inactivity, as is commonly implemented by websites featuring sessionmanagement.

There may be a system file ratings.txt, parallel to links.txt in eachdirectory, containing all contributed ratings for the links inlinks.txt. Information stored in ratings.txt for each link includes theemail address of each contributor, and the contributed rating. When anew rating is contributed, an entry is appended to ratings.txt. If thereis already a rating from that email address, it is replaced with the newone. A new average rating is computed, and the updated average ratingand contributor count are entered into links.txt as properties for theaffected link.

Another system file, reviews.txt, also parallel to links.txt, resides ineach directory and contains all contributed “link reviews”. Informationstored for each link includes the email address of each contributor, andthe contributed review. When a new review is contributed, it is appendedto reviews.txt, replacing any previous review from that email address.

5.1.21 Link Database Details

Links may be stored on the server in the following simple ASCIItext-file format:

ID | KEY | URL | PropertyName:Value | PropertyName:Value | . . . ID |KEY | URL | PropertyName:Value | PropertyName:Value | . . . . . .

This format uses explicit property names which are convenient whenspecifying sparse subsets of all possible properties (and also moreclear for describing the invention). An alternative is the use of afixed-format record in which the property names are implied by theirfield position within the record.

The ID is a unique integer assigned to the database record. The IDtherefore uniquely identifies the record and can be used to identify itin various contexts, such as in the URL for indirect links.

For example, a link to a Web page about the “W3K” website could appearin the link database (in one long line which is broken for claritybelow) as

23 | W3K | <<http://www.w3k.org>>| Date:2-Sep-99 | Context :/Education/Technology/W3K | Level:All | Rating:5 | RatingCount:7 | Hits:20 | Installs: 4 | Owner : Julius Smith | Group : CM_DSP | OwnerEmail :jos@w3k.org

In addition to link databases, there is preferably a user databaseholding information such as a list of IP addresses authorized for thatemail address, whether the user wants to receive the W3K newsletter, thelist of groups to which the user belongs (being a “trusted user” meansbelonging to the “trusted” group), and information logging anyinappropriate use of the service such as submitting offensive links.(See the system for dealing with “trolls” at http://www.slashdot.org foran example system.)

5.1.22 Example Link Properties

Example PropertyNames and their meanings are as follows:

TABLE 3 Property Meaning Level Educational level of the link, if not arange (1–100, All) MinLevel Lower bound of educational level range, ifapplicable MaxLevel Upper bound of educational level range, ifapplicable FullTitle Contents of URL's HTML <TITLE> tag in quoted stringDescription Description of link by submitting user Date Date link wassubmitted by user Type Type of information (Encyclopedia, Tutorial,Book, Course, . . . ) Language English, French, German, Spanish, . . .Suitability Similar to rating system used in the “V chip” for televisionContext Context path (when handling many contexts per database file)Synonyms List of equivalent phrases separated by ‘|’. Order isimportant. Hits Number of times link accessed by browsing InstallsNumber of documents link has been installed in Rating Quality rating asa number from 1 to 10 RateCount Number of users contributing ratingsisNew 1 if Date is sufficiently recent isPopular 1 if Hits is largerelative to other links OwnerEmail Email address of link contributorReceiveMail 1 if link contributor wants our newsletter Groups List ofowning groups separated by ‘|’ User1 Property defined by user User2Property defined by user . . . . . .

The properties can be used to limit the range of links installed by alink installation. For example, a certain educational level range can bespecified, or links only of a certain type may be specified. Restrictionto links contributed by the owner or owning group is also easilyspecified. KEYs will match occurrences of any case by default. When alink is installed in a user's document, the user's original case ispreserved in the anchor text. KEYs may be entered in singular form sincethe string matching algorithm will match will ignore a trailing ‘s’. AKEY is either a simple word or a phrase consisting of words separated byunderbars, e.g., Funk_&_Wagnalls_Knowledge_Center. A word may notcontain certain “meta-characters” such as “|” or “#” which have systemmeanings, and all such meta-characters are stripped out by a regularexpression (in Perl) on input. Similarly, context names must be “legal”UNIX file names after whitespace has been converted to underbars ‘_’,since the preferred embodiment uses a UNIX directory tree correspondingto at least part the context hierarchy. Restriction to legal filenamesis easily relaxed by encoding the directory names in hexadecimal, as anexample, or using the special character encodings of HTML. The stringmatching algorithm used in link installation “folds” the input case to“lower” and replaces underbars and hyphen with spaces in stringcomparisons. As a result, KEYs in text submitted for link installationcan have any case and can include underbars, hyphens, or spacesseparating words in the keyword phrases, yielding the same matchingresults in all such cases. In the above example, the link name isfunctionally equivalent “funk wagnalls knowledge center” for purposes ofstring matching. To include special characters where necessary, namesmay be quoted, as in‘Funk & Wagnalls Knowledge Center’

In the case of quoted names, string-matching is exact. Other detailsregarding string matching for link installation may be seen in theexample of Appendix A.

5.2 Single-Computer Implementation

The present invention can be adapted equally well to single-computeroperation, requiring no network connection. In this case, the user caninstall a link database application from a CD-ROM, for example, in thefashion typical of many software products for personal computers. Allfunctions formerly described as being provided by a Web browser and theremote link-installation and database server can be provided by theinstalled application. A Web version, if available, can serve to providea supplementary collection of links.

There are several advantages to this mode of operation:

-   -   Since all data and software are local, response time can be        greatly improved relative to use over the Internet.    -   A link database application may take advantage of native        graphical user interface (GUI) facilities on the personal        computer, which are typically more advanced than the        platform-independent HTML and Web-browser facilities.    -   Since link database extensions may occur on the local hard disk        instead of on a remote website, security requirements are        alleviated, and user privacy is enhanced, especially for        “private” database directories.    -   The link databases are not constantly changing, particularly the        ratings, thereby automatically giving repeatable results on        repeated link installations.    -   The link databases can be customized by manually setting        alternative link orderings, and eliminating unwanted alternative        links.

The following implementation differences apply to the single-computerembodiment:

-   -   Instead of one master link database directory, there may be two        parallel link database directory trees having a common directory        structure. The first may be “read only” so that it can be        distributed and used on a CD-ROM, for example, while the second        is “writable” and contains any user-developed databases, as well        as the temporary “system files” generated during use of the        system. The writable directory tree will normally reside on a        local hard disk.    -   In operation, the writable directory is searched first so that        it takes precedence over the read-only directory,    -   Logically, the links.txt files in the writable and read-only        directory images are treated as one file, with the read-only        version being appended to the writable version.    -   Links on the CD-ROM may be “deleted” by adding a corresponding        entry for them in the writable directory tree consisting of        exactly the same keyword or phrase, the same URL, and the single        property “DELETED”. Read-only directories cannot be deleted or        renamed, but they can be excluded from link searches in the        normal way (which applies also to the corresponding directory in        the writable tree, if any, since they are logically the same        directory).    -   Link database updates may be obtained over the Internet and        installed locally to keep the single-computer software up to        date. To facilitate this process, it is convenient to maintain        on the server listings of database directories and contents for        each software release. During an update, the server can traverse        the link database directory, compare against the listing        applicable to the user's current release, and generate an        incremental update to bring the user up to the latest state. The        incremental update is installed in the writable database        directory on the user's local computer, automatically shadowing        any older corresponding information on the CD-ROM. Updates may        be obtained at any time to obtain the latest links. Information        can be stored locally on the user's machine to enable each        update to be incremental relative to the previous update as        opposed to the latest official release.    -   URLs submitted in the “Text or URL” textfield of the        link-installation submission form may also include “file:” type        URLs.

It may occur that the user has locally extended the link database in away that conflicts with the server's extensions since the time of theuser's release or last update. The directory path, keyword or phrase,and URL all have to be identical to create a link conflict, and soactual conflicts can only occur in link properties. Link rankings can ofcourse change at any time, and this is normal. However, since locallyinstalled ranking information may be a rating override by the user(rather than the result of a previous upgrade), it is not necessarilycorrect to overwrite the locally installed rating properties. Similarly,other properties may have been added by the user to fine tune linkinstallation results. During installation of the incremental update, theuser may be given a choice of whether or not to accept conflictinginformation from the incremental update on a link by link, or propertyby property basis. The default action may of course be to avoidoverwriting any user-developed information, and the default upgrade canproceed in this mode. In the default mode, all conflicting links can beinstalled in a third parallel directory tree for later inspection by theuser. Another means for avoiding conflicts is to rename any preexistingdirectories containing user modifications (by adding a private suffix toits directory name, say) before carrying out an update.

5.3 Educational Levels

The educational level of a definition is a number indicating howadvanced the material is. Authors generally wish to minimize theeducational level as much as possible consistent with the intendedaudience, the material being presented, and the desired length of thedocument.

Every definition (link) is assigned an educational level. A normalizededucational level may be provided manually by the link contributor as anumber between 0 and 100, with the number being loosely interpreted as“years of education likely required” for someone specializing in thesubject. When no manual assignment is made by the link contributor, alevel is automatically computed which interpolates the manually assignedlevels that do exist.

5.3.1 Automatic Assignment of Educational Levels

The automatically assigned level of a definition is computed by firstcomputing an integer “raw level” for the definition based purely on ananalysis of definition interdependencies, followed by the computationand assignment of a “normalized level” which maps each raw level to thepreexisting manually assigned level when it exists.

The raw educational level is defined as 1 plus the maximum raweducational level of all referenced definitions, where a definitionreferencing no other definitions is assigned a raw level of 1. Areferenced definition here means any server-resident link occurringinside the definition's document. All links outside the server areassigned a level of zero (to avoid having to process external documents,all their sublinks, etc., in a potentially huge recursion over theinternet). In a definition document which refers only to outsidematerial, which would receive an automatically assigned raw level of 1,it is the submitting author's responsibility to reasonably assign itseducational level manually when submitting it to the server. Forwardreferences in a document can be marked as such to prevent them fromartificially elevating the automatically computed level.

In the preceding paragraph, a “definition document” means the pagepointed to by the definition's URL together with all informationreachable from the definition page on the same website by followinglinks. Thus, as an example, the definition document corresponding todefinition URL http://www.w3k.org/includes the contents ofhttp://www.w3k.org/index.html together with any HTML (or other format)content reachable by following links within index.html, such ashttp://www.w3k.org/about.html, which are at the same site, that is,expressible using URLs starting with http://www.w3k.org/.

In addition to setting an appropriate educational level when possible,documents may mention any specific recommended prerequisites at theoutset, providing links whenever possible, so as to better orient thereader. The often-used “list of keywords” appearing below an article'sabstract, after being automatically linked by the present invention, canprovide a good first set of background links. However, an explicit listof prerequisite topics, automatically linked to top-ranked tutorials bythe present invention, can provide a more systematic and preferableapproach to prerequisites.

5.3.2 Normalizing Numerical Educational Levels

Educational levels are normalized to make them more intuitive to use.Normalization is a process which recomputes automatically assignededucational levels so as to make them fit more naturally among themanually assigned levels.

Raw numerical levels are integers which are bounded below by 0 andunbounded above. The raw level of any document is at least 1 greaterthan the maximum level among all documents it references. As automaticlevel assignment proceeds through a large collection of documents,levels of advanced writings can tend toward very large integers. As aresult, the raw level number is difficult to interpret. Normalizationcan be easily accomplished using a piecewise-linear mapping from theraw-level scale to some “standard level” scale.

The standard level scale used at the server may be loosely based on thenumber of years of education “likely required” to understand thedocument for someone taking a direct educational route to the materialin the given context. It is analogous to a “par score” in golf, whichdefines the average number of “strokes” required to complete the course,for a good player. Such a numbering scheme obviously becomes more andmore debatable at levels above 14 or so (middle undergraduate level)where curricula are not uniformly standardized. In fact, it is common inmany technical fields to constantly work toward moving level 17materials (beginning graduate level) down to level 14 or even below,meaning the “ideal” educational level is itself a moving target.

A nominal listing of normalized educational levels is given in thefollowing table:

TABLE 4 Numerical Named Range Range 0–1 Preschool to 1^(st) grade 1–21^(st) to 2^(nd) grade 2–3 2^(nd) to 3^(rd) grade 3–4 3^(rd) grade 4–54^(th) grade . . . . . . 12–13 12^(th) grade 13–14 College Freshman16–17 College Senior 17–18 1^(st) year graduate student 20–21 4^(th)year graduate student . . . . . . 100 Arbitrary maximum level

To find the nonlinear mapping necessary for level normalization, certaindocuments need to be assigned a “known standard level”, such as “8^(th)grade.” An obvious choice for such documents would be those occurring inactual standardized courseware. A few such documents spread out betweenzero and the maximum level are sufficient, but preferably there is atleast one per year, to make the mapping reasonably accurate. With thisinformation, a piecewise-linear mapping from raw level to standard levelcan be constructed which takes the automatically computed levels of theknown-standard-level documents to their known standard levels. Thus, thepiecewise linear mapping will have “break-points” at the level of eachstandard-level document.

For purposes of level normalization, a definition can be schematicallyrepresented by a list of numbers (the raw levels of all referenceddefinitions) to which a higher number must be assigned (the definition'sraw level). For example, two definitions D1 and D2 might appearschematically in this way as follows:D1(20): 13, 14, 18, 19D2(19): 17, 14, 18

Here, the number in parentheses (20, for Definition 1) is thedefinition's level, while the numbers following the colon ‘:’ give thelevels of all referenced definitions, not including forward references.

To keep track of the specific definitions providing each referencedlevel, let's extend the above notation to include definition number:D80(20): D2(13), D5(14), D44(18), D45(19)D81(19): D9(17), D5(14), D44(18)

Thus, in this example, definition node 80 is assigned a raw educationallevel of 20 which is consistent with the fact that its documentreferences definitions 2, 5, 44, and 45 which have been assigned rawlevels 13, 14, 18, and 19, respectively.

Forming a Directed Graph Expressing Educational Level Relations

From the above data structure, it is now straightforward to form adirected graph in which each node of the graph corresponds to adefinition, and a reference to another definition can be visualized asan arrow (also called an “edge” of the graph) pointing from thereferencing node to the referenced node. (The arrows can alternativelybe taken to all point in the other direction, from the referenced nodeto the referencing node.)

The problem of assigning consistent educational levels can now be seento be equivalent to the general problem of ordering the nodes of adirected graph so that every path through the graph traverses nodes in amonotonic numerical order. This type of ordering is known as atopological sort, and there are standard algorithms in computer science,such as Dijkstra's algorithm, for this purpose.

Resolving Cycles

It is well known that a directed graph can be topologically sorted ifand only if it is acyclic, meaning there are no cycles in the graph.Standard topological sorting algorithms just work when there are nocycles, and when there are cycles, they are detected and reported aserrors, leaving it to the user to “break the cycle” in some way.

Cycles can be caused inadvertently in documents by use of forwardreferences. For example, in a level 12 document about the calculus, itwould be quite natural to mention some calculus applications such assolving problems in elementary mechanics (which is level 13 at a typicaluniversity, requiring calculus as a prerequisite). To address thisproblem, a mechanism is provided for authors to mark forward referencesin documents, so that forward-reference links are ignored in thecomputation of educational level.

Algorithm for Educational Level Assignment

An algorithm for educational level assignment can now be described asfollows:

-   -   1. A directed graph is constructed by traversing all definition        nodes and building a tree in which each node contains a list of        pointers to other nodes. Each node corresponds to a definition,        and each pointer points to a referenced definition. Let the        definition nodes be arbitrarily numbered from 1 to N. This will        be called the “lexical ordering” of the nodes, and it need not        change.    -   2. Using a topological sort algorithm on the directed graph,        each node is assigned a second integer corresponding to its “raw        educational level. Nodes having no references (no “incoming        arrows”) are assigned a raw level of 1. A node having one or        more references is assigned a raw level at least 1 greater than        the raw level of all referenced nodes. (Manual assignments used        for normalization are ignored during the topological sort.)    -   3. Use the raw level assignments together with the manually        assigned normalized levels to construct a piecewise-linear        mapping from raw to normalized educational level for all nodes.

A Perl program implementing the above steps is given in Appendix D.

Non-Monotonic Manual Level Assignments

There is nothing in the system to prevent manually assigned educationallevels from being “out of order” relative to the raw assigned levels.For example, suppose document A has a raw level of 200, while documentB, which references document A either directly or indirectly, has a rawlevel of 250. Suppose further that document A has a manually assignedlevel of 40 while document B has a manually assigned level of 30. Sincethe manual ordering is the opposite of the reference-based ordering, aconflict occurs, and the piecewise linear map which takes raw tonormalized levels will have a segment with negative slope, which doesn'tmake sense.

There are several possible ways to address this issue:

-   0. The manual assignments can be forced to be monotonic by adjusting    them so that the minimum piecewise-linear mapping slope is zero (or    some small positive number). In the above example, the normalized    level of B could simply be thrown out on the simple grounds that    since B references A, it is by definition at a higher level, so that    its manual level cannot be allowed to be set lower than that of A.    It could alternatively be set to the same level as A. A could also    be compared with other documents at comparable raw levels to see if    its manually set level is unusually high, and, if so, it can be    rejected as an “outlier”. The automatic normalization system does    not need many manually set levels, so it is preferable practice to    throw out any that seem suspect for any reason.-   1. Manual level assignments can be allowed only for values up to,    say, 18, forcing all higher levels to be extrapolated via automatic    assignment. Extrapolation may be determined by normalizing the    highest raw level to 100, and other values would function as well.    Alternatively, the slope of the mapping leading up to normalized    level 18 can be estimated, and higher raw levels can be normalized    to preserve this slope.-   2. A slightly more sophisticated version of the previous solution is    to “fit a monotonic curve” through the manual level assignments. To    see how this works, plot N(i) versus R(i) in the Cartesian plane for    all i, where i ranges over all definition links in the system, R(i)    is the raw level assigned to definition i, and N(i) is the    normalized level manually assigned to definition i, if any. If N(i)    is not assigned, do not plot the point. Since there can be any    number of documents with the same raw level R(i), there may be many    values of N(i) for a given value of R(i) as i ranges over all links    in the database. For each R, a range of normalized values may be    covered by N. Such a plot of N versus R can be called a “scatter    plot.” For simplicity, suppose both R and N are normalized to range    between 0 and 1, so that the plot of N versus R in the Cartesian    plane starts at (0,0) and terminates at (1,1). Ideally, this    distribution of points in the plane will resemble a blurry line at a    45-degree angle (or perhaps a concave or convex curve instead of a    straight line, etc.). Well known curve fitting methods, such as    linear regression, cubic splines, Bezier curves, and least-squares    polynomial fitting can be used to fit a monotonic curve through the    “scatter-plot” of N versus R.-   3. A more refined version of the previous solution is to replace the    2D scatter plot by a 3D histogram. As in the 2D case, the horizontal    axis is R and the vertical axis is N in the plane; however, the    third dimension for each plane coordinate (N,R) is now the “number    of definitions having manual level N and raw level R”. The scatter    plot resembling a blurry monotonic planar curve in the previous    solution now becomes a raised histogram following the same curve.    However, the third dimension allows seeing where “most” of the    manual ratings lie, and a curve-fitting procedure can try to “follow    the ridge” in the histogram. There are numerous curve fitting and    “hill climbing” methods known those skilled in the art that would be    straightforward to apply here.-   4. Certain manual level assignments can be given priority over    others, such as those produced by an educational standards body,    educational institution, or professional society. Deferring to these    assignments in the event of a conflict may resolve it in some cases.-   5. An expert in the field can study the level assignments and make a    recommendation for reassignment of the manual normalized levels as    seems right.

In any case, when a manually set normalized level is thrown out orreassigned, the owner of the modified link record is preferably notifiedvia email. In the current preferred embodiment, the combination ofsolutions 0 and 1 is employed, but more sophisticated solutions areanticipated to become preferable as the link database grows.

It is informative for users to see a histogram of the number ofdocuments having a certain normalized level versus normalized level.Such a histogram can indicate to users how significantly the number oflinks installed will change as the minimum and/or maximum educationallevel are adjusted.

Educational Levels as Context Limiters

Note that level assignment helps to disambiguate between relativelyadvanced and elementary contexts. In one actual example encountered bythe author, the proof of “Euler's theorem” contained the use of thephrase “positive real number.” The term “positive real” existed in thedictionary for the same context, but at a much more advanced level. (Itwas entered as short for “positive real function” which is amathematical property of functions in the complex plane characterizing“passive” driving-point impedances in the context/Engineering/Electrical/Classical_Circuit_Theory). Since links to highereducational levels are normally suppressed when installing links, themisleading link would not occur. Other solutions to this problem include(1) requiring the whole phrase “positive real functions” for a matchwith the more advanced topic, (2) splitting contexts so as to separateelementary complex variables and more advanced network theory, and (3)supplying a trivial home page for “positive real number” which thenwould shadow “positive real” in this case.

Context Dependency of Educational Levels

Since a link to a particular document may be repeated in any number ofcontexts, its manually assigned educational level may be a function ofthe field associated with that context (such as a high-level parentcontext). For example, in an engineering curriculum, study of the “phasevocoder” (a tool for “stretching” sound in time, among other uses) caneasily occur at normalized level 16 (a college senior with a goodundergraduate background in signal processing). On the other hand,within a computer music graduate curriculum, the “phase vocoder” topicmay be set at level 18 or 19 so that the Music Ph.D. student has time topick up necessary signal processing prerequisites in the electricalengineering department. (In the golf analogy, 16 is “par”, whilenon-engineering majors (“less experienced players”) may receive a 2 or 3stroke “handicap”.) When levels are fine-tuned in this way, the relevant“context synonyms” previously described may need to be broken. Forautomatic level assignments to follow context-sensitive normalizedlevels, it is necessary for documents to either specify the context ofthe link (as described below), or provide the context of the documentcontaining the link, such as is easily provided in HTML “metadata”. Insummary, a single document may have a different normalized educationallevel assigned to it in different contexts.

A convention for handling multidisciplinary documents can be that thelevel of the document is set according to the portion of the documentwhich properly belongs in the context to which it is assigned. Adocument requiring expertise in three fields, say, could then receivethree different levels, one in each context, where the level in eachcase depends only on the portion of the document pertaining to thatfield. As an example, consider a paper on the legal issues of patentinggenetically engineered life forms; the paper can be placed in thecontext hierarchy in at least two places, under /Legal/Patents, andunder /Science/Biology/Genetic_Engineering (which, by the way, could besynonymous with /Engineering/Genetic_Engineering). Under /Legal/Patents,its level is set according to the level of legal background required.Under /Science/Biology, its level is set according to the level ofknowledge required to understand the technical aspects of the article.

Since link properties can be added by the user, the above example can beextended to include a secondary level specification. For example, whenfiling the paper under /Legal/Patents, it can be given two additionaluser-defined propertiesSecondaryContext: /Science/BiologySecondaryLevel: 14and the filing of a link to the paper under/Science/Biology/Genetic_Engineering can have the two extra propertiesSecondaryContext: /Legal/PatentsSecondaryLevel: 16for example.

An alternative mode of treatment for multidisciplinary orcross-disciplinary documents is to assign a manual level to the documentwhich represents the number of years of education likely required forunderstanding assuming one first obtains a typical background in thecurrent context. That way, the level numbers of links in a particularfield are most meaningful for people in that field. Since people in thefield are most likely to be using the links for that field, it makessense for the numbers to be best adapted to their needs.

The system of the present invention allows for many choices ofnormalized level scale, and the scale can be changed at any time byresetting the manually set levels. A link contributor may, for example,perform a property-based link database search which collects togetherall editable links at a particular educational level, and changes allthe levels to a new value in one edit operation on the selected set.

Example of a Very High Educational Level

A specific example of a particularly high educational level is“superstring theory” which is a current “hot topic” in theoreticalphysics. Understanding a recent conference paper on this topic mightrequire several prior recent papers to be read and understood, and thesein turn might require the equivalent of a basic textbook on superstringtheory, which would require a solid grounding in quantum field theory,which requires a basic quantum mechanics background, which requires afew years of physics and math at the college level, and so on. It isdebatable how long it should take a “good student” to get through such apath of study in order fully grasp the end concepts, but this questioncan be decided by educators and professional societies. Since normalizededucational levels are ultimately determined by manual assignment, theautomatic assignment system will conform to their decisions.

Curricula “Critical Path” Identification and “Education On Demand”

As educational curricula become “finer grained”, the normalizededucational level numbers may go down over time as shorter and shorter“critical paths” to particular advanced topics are identified. Curriculacan in fact be based precisely on such identified paths, or evenautomatically generated from them. This is a foreseeable use of thepresent invention. Specifically, a student can choose a set of skillsand topics he or she wishes to master, and plunge in immediately on themost advanced level, clicking on links whenever a word or phrase is notunderstood. After enough clicks, a level is reached where the materialis digestible, and the student can eventually work back up to thedesired level. This is in contrast to the usual program of beginningwith elementary preliminaries which can seem unmotivated to the student.Needed educational prerequisites can be “paged in” as needed on ademand-driven basis (to use an analogy with “demand paging” in computerscience). Significantly, unnecessary educational prerequisites can bebypassed entirely.

Demand-driven education can be more motivating to students prefer towork with an end goal in sight. Since everything studied is motivated byan attempt to understand a more advanced document which accomplishes atangible desired goal (such as “stretching” sound without changing itspitch in the case of the phase vocoder), it can always be clear to thestudent, for example, “what is this for,” and “how are we going to usethis.” It further provides a “natural selection mechanism” foreducational materials, omitting required study of anything not needed tofathom the specifically chosen advanced materials on the desired track.

Application to Automatic Teaching and Certification

In a computer-assisted curriculum along these lines, the student mayhave to answer exam questions at the end of each document which serve toverify and reinforce the student's understanding. In the end, a courseof study could result in a collection of automatically generatedcertificates for the topics covered, and job requirements could bestated in terms of certification levels on specific topics. There areobvious issues associated with proctoring exams in such a system, butthere exist traditional solutions as well as more novel technologicalsolutions using, say, a simple camera attached to the computer with aviewing angle large enough to include the keyboard.

Such a mechanized approach to self-paced educational certification has afew obvious disadvantages relative to more traditional educationalmethods, especially given the limited “virtual reality” capabilities ofpresent day computers. However, it can provide a very efficient way to“tool up” on a technical topic, particularly for the time-limitedemployee, the spare-time student, or the bright young learner in adeveloping country seeking salable job skills in the global informationeconomy.

5.4 Preferred Link Targets

Preferably, each concept is given its own “home page” on the Web whichapproaches the subject in a top-down way, addressing the widest possibleaudience, and directing all interested readers to the most appropriatefurther information for them. All-encompassing home-page styledefinitions are likely to emerge as the “best definition” in auser-ranked list. Being designated the “best definition” for a topic issignificant in that, in some modes of operation, only the “best”definition is available to the end user in installed links.

Example “topic home pages” include one on the Kalman filter at<<http://www.cs.unc.edu/˜welch/kalmanLinks.html>>and the “Digital Audio Resampling Home Page” located at<<http://www-ccrma.stanford.edu/˜jos/resample/>>

Another advantage of top-down, general-interest, home pages on a giventopic is that its minimum educational level may be set low, allowing thelink to be installed in a greater variety of materials, while the expertcan skip over the introductory tutorials and proceed directly to themode advanced material of interest. For this reason, the preferredembodiment supports specifying a range of educational levels for asingle document. A well designed topic home page might span levels fromhigh-school all the way out to the research frontier. An example websitecovering such a large range (although not devoted to a single topic) isthe Physics 2000 website at<<http://www.Colorado.EDU/physics/2000/>>5.4.1 Generating Link Targets in a Uniform Format

A useful means for generating link targets is to write a LaTeX documentwhich explains one “concept” per section. The title of the section maybe the word or phrase being defined. The first occurrence of theconcept's name may be emphasized using the LaTeX command /emph{ }. Theutility latex2html can then be used in a normal fashion on such a“concepts file” to create a separate HTML file for each section, and thehypertext index generation capability of latex2html can be used togenerate the associated link database (dictionary file). Alternatively,a dictionary can be generated directly from the HTML using the widelyavailable Perl modules LWP and HTML (see, for example, the Perl Cookbookby T. Christiansen and N. Torkington, O'Reilly, 1998). A Perl script forthis purpose is listed in Appendix B. The dictionary file so generatedmay be submitted to the link database server to conveniently contributelinks to all the newly created concept home pages on the Web. (Thescript is written to retrieve all files under a URL by following links,thereby providing a starting point for a utility which creates adictionary file from any website on the Web.)

The LaTeX command /section{ } can be replaced by an invocation of thefollowing more convenient macro:

\newcommand{\ConceptSection} [2] { \section{#1} \index{#1}\begin{htmlonly} \rawhtml{<!-- W3K_PROPERTIES: ‘#1’ #2 −−>}\end{htmlonly} }

This macro is called with the section name as usual, but additionalproperties may be specified in the second argument, and these are passedto the output in an HTML comment which may be interpreted by the scriptwhich creates a dictionary file from the HTML files (a starting point isgiven in Appendix B). (A more elegant solution, feasible when XML iswidely supported by Web browsers, is to define an XML tag for each linkproperty.) Context properties found in the HTML comments may betranslated to PATH directives in the dictionary file. An alternative useof properties embedded in link target files is that, when using indirectlinks, link properties do not have to be included in the link databaseat the link server.

As an example, a new section could begin as follows:

\ConceptSection{Derivative}{Level:12 Context: /MathematicsSynonyms:Differentiation}{ The \emph{derivative} with respect to $x$ ofthe continuous function $f(x)$ is defined by the \emph{limit} . . . }and a related example might be

\ConceptSection{Derivative}{Level:11 Context: /Financial/Investing}{ A\emph{derivative} is a financial instrument derived from an underlyingsecurity such as . . . }

Note how the use of the Context property can be extremely important forobtaining the desired results. If the Context property is not specifiedfor a link, it may default to the path of the database directory inwhich the link resides. The Context value All can be specified in a linkentry by trusted users to enforce only one meaning of a term across allContexts. Such treatment could be appropriate for trademarks, forexample. Since the top level of the link database directory tree isContext independent, link entry at that level can be restricted totrusted users.

5.5 Guiding Link References

In the previous example, properties were used to specify the context andeducational level of a link target. Properties can similarly bespecified in documents submitted for link installation in order to guidelink installation. Thus, the document receiving links can call for linksof a certain type rather than having to specify all aspects of linkinstallation in a separate script or over the browser interface at theserver.

As an example, in a document using the term “derivative,” the contextmay be specified as follows:The /kref{derivative}{Context:/Mathematics} with respect to $x$ of thecontinuous function $f(x)$ . . .where the kref macro might be defined along the following lines:

\newcommand{\kref} [2] { \emph{#1} \begin{htmlonly} \rawhtml{<!--W3K_PROPERTIES: ‘#1’ #2 −−>} \end{htmlonly} }

A linked reference can be marked as a “forward reference”, for example,viaThe /kref{derivative}{Context:/Mathematics ForwardReference} withrespect to $x$ of the continuous function $f(x)$ . . .in order to avoid having it affect the educational level of the currentdocument. While these examples pertain to LaTeX submission format,preparation of plain HTML submissions is specified implicitly as well,since LaTeX is compiled into HTML in this application.5.6 Converting Browser Bookmarks to Dictionaries

The Perl script in Appendix C can be used to convert the “Favorites”folder containing Internet bookmarks for Microsoft Internet Explorer 5to the dictionary file format described above. The inexpensive utilityprogram LinkSync (<<http://www.bluesquirrel.com>>) can be used toconvert Netscape Navigator bookmarks to MSIE format (and vice versa).Many “web surfers” have valuable hierarchically organized “linkcollections” in their browsers which might usefully be converted todictionary files that can be submitted to the link installation server.Hierarchy is preserved by creating context paths as needed.

6 REFERENCES CITED

6.1 U.S. Patent Documents

-   U.S. Pat. No. 4,982,344; Jan. 1, 1991; Daniel S. Jordan;    Accelerating link creation    6.2 Other Publications-   L. Carr, “The link fifty years on: A personal view of hypertext    linking,” SIGWEB Newsletter, vol. 8, pp. 41-43, February 1991.-   L. Carr, D. De Roure, W. Hall, and G. Hill, “Implementing an open    link service for the worldwide web,” World Wide Web, vol. 1, no. 2,    pp. 61-71, 1998.-   S. Hitchcock, “Open journal project: final report to elib,” tech.    rep., Multimedia Research Group, University of Southampton, November    1998.-   H. Wells, “World brain: The idea of a permanent world encyclopedia,”    in Encyclopédia Française, 1937.

1. A system for automatically linking key phrases in submitted text, thesystem comprising: a computer processor; a database containing storedhypertext links and stored key phrases, wherein each of the storedhypertext links is associated with one of the stored key phrases,wherein at least one of the stored key phrases is associated with aplurality of the stored hypertext links, and wherein at least two of thestored hypertext links correspond to different contexts for the samestored key phrase; text input means for receiving the submitted textfrom a submitter; matching means for finding an occurrence of at leastone of the stored key phrases in the submitted text, thereby determininga set of one or more found key phrases; link retrieval means forretrieving from the database one or more found hypertext linksassociated with the set of one or more found key phrases; and outputmeans for communicating the found hypertext links to the submitter. 2.The system of claim 1 wherein at least two of the stored hypertext linkscorrespond to mutually competing definitions associated with the samestored key phrase.
 3. The system of claim 1 wherein the databasecomprises a plurality of databases, each containing stored hypertextlinks and stored key phrases associated with at least one of the storedhypertext links, the system further comprising database-selection meansfor selecting one or more databases from the plurality the databases tobe used by the matching means.
 4. The system of claim 1 furthercomprising subset specification means for specifying a subset of thestored key phrases and the stored hypertext links, thereby determining astored subset, and wherein the matching means searches the submittedtext for an occurrence of stored key phrases belonging to the storedsubset.
 5. The system of claim 4 wherein the subset specification meansfurther comprises browsing means for the submitter to select stored keyphrases and stored hypertext links while browsing the database.
 6. Thesystem of claim 4 wherein the subset specification means furthercomprises means for specifying the stored subset based on a linkproperty assigned to the stored hypertext links.
 7. The system of claim6 wherein the link property corresponds to a rating.
 8. The system ofclaim 6 wherein the link property corresponds to a link ownership. 9.The system of claim 6 wherein the link property corresponds to aresource type.
 10. The system of claim 6 wherein the link propertycorresponds to a viewer suitability.
 11. The system of claim 6 whereinthe link property corresponds to an educational level.
 12. The system ofclaim 11 further comprising means for computing the educational level ofa stored hypertext link automatically based on information found byfollowing the stored hypertext link.
 13. The system of claim 11 furthercomprising a link level submission means for submitting a manuallyassigned educational level for at least some of the stored hypertextlinks.
 14. The system of claim 13 further comprising means forautomatically computing a normalized educational level for a storedhypertext link of unknown educational level.
 15. The system of claim 6wherein the link property corresponds to a context.
 16. The system ofclaim 15 wherein the stored subset is ordered according to a specifiedcontext order, and wherein the matching means searches the submittedtext for occurrences of stored key phrases belonging to the storedsubset in the specified context order.
 17. The system of claim 1 whereinthe output means further comprises means for modifying the submittedtext to include at least one of the found hypertext links and bereturned to the submitter as output text.
 18. The system of claim 1wherein the text input means further comprises means for receiving adocument containing the submitted text.
 19. The system of claim 1wherein the text input means further comprises means for receiving thesubmitted text from a web browser.
 20. The system of claim 19 whereinthe output means further comprises means for transmitting the foundhypertext links from a server to a web browser.
 21. The system of claim1 wherein the matching means further comprises match-limiting means forlimiting the set of one or more found key phrases in the submitted text.22. The system of claim 21 wherein the match-limiting means furthercomprises means for limiting matches to emphasized found key phrases inthe submitted text.
 23. The system of claim 21 wherein thematch-limiting means further comprises means for limiting matches to afirst occurrence of each found key phrase in the submitted text.
 24. Thesystem of claim 1 further comprising means for determining an orderingof stored key phrases, wherein the matching means searches the submittedtext for an occurrence of one or more stored key phrases in accordancewith the determined ordering of the stored key phrases.
 25. The systemof claim 24 wherein the matching means further comprises means forinhibiting the finding of previously found key phrases while searchingthe submitted text for occurrences of stored key phrases in thedetermined ordering.
 26. The system of claim 1 wherein the output meansfurther comprises multiple-link handling means for processing a foundplurality consisting of a plurality of the found hypertext linksassociated with a found key phrase in the set of one or more found keyphrases.
 27. The system of claim 26 wherein the multiple-link handlingmeans further comprises means for producing an indirect hypertext linkpointing to a page containing the found plurality.
 28. The system ofclaim 26 wherein the multiple-link handling means further comprisesmeans for transmitting the found plurality to a web browser.
 29. Thesystem of claim 26 wherein the database comprises means for associatingat least one link property with each stored hypertext link.
 30. Thesystem of claim 29 wherein the multiple-link handling means furthercomprises means for choosing one chosen hypertext link from the foundplurality based on at least one link property assigned to each of thestored hypertext links in the found plurality.
 31. The system of claim30 wherein the link property corresponds to a rating.
 32. The system ofclaim 1 wherein the input means further comprises means for receivingthe submitted text as plain unformatted text.
 33. The system of claim 1wherein the input means further comprises means for receiving thesubmitted text in HTML format.
 34. The system of claim 1 wherein theoutput means further comprises means for transmitting the foundhypertext links in HTML format.
 35. The system of claim 1 wherein theinput means further comprises means for receiving the submitted text inLaTeX format.
 36. The system of claim 1 further comprising means fortransmitting the found hypertext links in LaTeX format.
 37. The systemof claim 1 further comprising link submission means for providingsubmitted hypertext links and submitted key phrases to the system; andlink adding means for adding the submitted hypertext links and thesubmitted key phrases to the database.
 38. The system of claim 37further comprising a level submission means for submitting a manuallyassigned educational level for the submitted hypertext links.
 39. Thesystem of claim 38 further comprising means for computing anautomatically assigned educational level for the submitted hypertextlinks, and further comprising means for processing marked forwardreferences in the submitted text so that the automatically assignededucational level is not affected by the marked forward references. 40.The system of claim 37 further comprising a hierarchy means for creatinga hierarchical structure for the database, wherein the hierarchicalstructure is based on a context property assigned to each of at leastsome of the submitted hypertext links.
 41. The system of claim 40further comprising a restricted hierarchy means for creating arestricted hierarchical structure based on the submitted hypertextlinks.
 42. The system of claim 40 further comprising a private hierarchymeans for creating a private hierarchical database structure based onthe submitted hypertext links.
 43. A method for finding key phrases insubmitted text and associating the found key phrases with foundhypertext links, the method comprising the steps of: specifying a set ofstored hypertext links and stored key phrases, thereby forming a set ofspecified hypertext links and a set of specified key phrases, whereineach of the specified key phrases is associated with at least one of thespecified hypertext links, wherein the specified hypertext links haveassigned contexts, and wherein the specified key phrases are arranged ina precedence order; receiving submitted text, wherein the submitted textcontains at least one key phrase that matches one of the specified keyphrases; searching the submitted text in accordance with the precedenceorder for matches of key phrases in the submitted text with one or moreof the specified key phrases, thereby determining a found key phrase foreach match; retrieving at least one found hypertext link from thespecified hypertext links that is associated with the found key phrase;and transmitting the at least one found hypertext link as output. 44.The method of claim 43, further comprising a step of receiving submittedhypertext links prior to the searching step.
 45. The method of claim 43wherein a longer key phrase appears before a shorter key phrase in theprecedence order, the shorter key phrase being contained within thelonger key phrase, thereby establishing a precedence of the longer keyphrase over the contained shorter key phrase during the searching step.46. The method of claim 43 wherein the submitted hypertext links areautomatically tested prior to the searching step.
 47. The method ofclaim 43 wherein the precedence order at least partly corresponds to theorder of the submitted key phrases.
 48. The method of claim 43 furthercomprising a step of selecting a subset of the submitted hypertext linksbased on one or more link properties prior to the searching step. 49.The method of claim 43 wherein the submitted hypertext links areorganized hierarchically according to a plurality of assigned contextsfor the submitted hypertext links, and wherein the specification furthercomprises specifying the set of hypertext links based on the assignedcontexts.
 50. The method of claim 43 wherein the specifying step furthercomprises specification based on a link property.
 51. The method ofclaim 50 wherein the link property is a context.
 52. The method of claim51 wherein the specification of the context automatically results inspecification of links in lower-level contexts.
 53. The method of claim51 wherein the specification of the context automatically results inspecification of links in higher-level contexts.
 54. A system forretrieving hypertext links corresponding to key phrases in text,comprising: a computer processor; a database for storing hypertextlinks, wherein each of the hypertext links is associated with a set ofone or more key phrases, wherein at least one of the key phrases isassociated with a plurality of the hypertext links, and wherein at leasttwo of the stored hypertext links correspond to different contexts forthe same stored key phrase; link selection means for selecting a subsetof the hypertext links, thereby forming a selected subset of hypertextlinks; text input means for receiving submitted text from a submitter;matching means for finding an occurrence in the submitted text of a keyphrase associated with a member of the selected subset of hypertextlinks; choosing means for choosing one or more hypertext linksassociated with the found occurrence; installation means for installingthe chosen one or more hypertext links in the submitted text to produceoutput text; and output means for returning the output text to thesubmitter.
 55. The system of claim 54, wherein the link selection meansfurther comprises means for selecting links based on link ratings. 56.The system of claim 54, wherein the database is organized hierarchicallyaccording to context, and wherein the link selection means furthercomprises means for selecting links based on their assigned context. 57.The system of claim 56, wherein the link selection means furthercomprises means for combining context dictionaries corresponding to aplurality of the contexts in the hierarchical database.